1984 by George Orwell talked exactly about this type of synario and I have quotes from the book and explanations that will answer your question about the benefits of mass surveillance.
The Party constantly watches all citizens for any sign of rebellion or thought-crime, but tries to appear kind and concerned rather than ruthless and invasive. It adopts the protective, reassuring persona of 'Big Brother' and the slogan:
"BIG BROTHER IS WATCHING YOU" Part 1, Section 1, pg. 3
Information Awareness Office- Wikipedia
One of the most important ways that the Party keeps citizens under surveillance is through the telescreens. They are found in all rooms belonging to Party members, and in public places. No one knows how often the Thought Police tap into any individual wire, it is therefore possible that they watch all screens all the time. Outer Party members can dim the sound and picture coming from their telescreen, but the screen never turns off. Only senior members of the Inner Party have the power to turn off the telescreen, but can only do so for short periods of time. Very few proles have telescreens, mostly because members of the Inner Party do not feel they pose a threat. For the proles who do own one, the telescreen is an expensive item that they might buy for the entertainment value.
In addition to telescreens, the police (not the Thought Police) also have patrols of surveillance helicopters that fly around peering into people's windows.
Your Smart TV is Spying on You- Fox News
Your Smartphone is Spying on You- CNN
The Party uses children to keep tabs on their parents. Through the Spies, children are trained to be devoted Party followers. The children are ferocious towards thought criminals and most adults over the age of thirty are afraid of their own children. Children are encouraged to eavesdrop and most weeks there is a story in the Times about a child hero who has denounced his family.
D.A.R.E. Program teaches children to narc on parents
Winston thinks about how dangerous it is to allow your thoughts to wander when you are in public or facing the telescreen. Your facial expressions are watched closely and the wrong expression can have dire consequences. For example, looking disbelieving when a victory is announced would be facecrime.
"Your worst enemy, he reflected, was your own nervous system. At any
moment the tension inside you was liable to translate itself into some
visible symptom." Part 1, Section 6, pg. 64
Facial Recognition Technology is Everywhere
The Party supervises all marriages, so as to avoid sexual desire between Party members. A committee has to approve a marriage, and they refuse permission if the couple give the impression of being attracted to each other.
Surveillance of the proles is limited. The Thought Police track down and eliminate the few proles who seem capable of becoming dangerous to the Party.
Even when Winston is at his desk at work, he is closely watched by the telescreen. When he finds the photograph, he must force himself to control his facial expressions and breathing. He even worries the quickness of his heartbeat will be picked up by the telescreen. When Winston was at the Chestnut Tree Café years ago and saw Jones, Aaronson and Rutherford, there was a sudden half a minute when something happened to the telescreens and they started playing a mocking piece of music, as if jeering at the three men.
A Party member's attendance at the Community Center is carefully checked. It is dangerous to spend any significant time alone. Party members are not supposed to have any spare time, and should only be alone when sleeping.
It is dangerous for Winston to walk in the prole area. If a patrol were to see him, they would stop and question him to check his papers, perhaps even reporting it to the Thought Police.
Winston is tempted to read the piece of paper while he is in the bathroom, but there is no place the telescreens watch closer than the toilet stalls.
All letters sent by mail are opened and checked by the mail service. There is no such thing as private mail.
Hint: The United States Postal Service needs a warrant to search packages...UPS and FedEx do not
In the open country there are no telescreens, obviously, but there are hidden microphones by which your voice can be picked up and recognized. Making a journey by oneself also tends to attract attention. Patrols freely hang around railway stations to check the papers of any Party members they find and interrogate them. To go a hundred kilometers or more, you need to get your passport endorsed.
O'Brien offers to lend Winston the dictionary as a way to give him his address. Although the government keeps an eye on everyone's movements, ordinary citizens know very little about where other Party members live. There are no directories; the only way to find out where someone lives is to ask them. O'Brien develops this plan and then gives Winston his address openly, in order to avoid suspicion. He writes the address on the paper right in front of a telescreen, where anyone watching can read what he is writing.
Winston and Julia realize that the one thing the Party cannot control is what people feel inside. The one thing they have not discovered is how to monitor what other people think. Winston thinks that within the walls of the Ministry of Love this may be different. He suspects they may use torture, drugs, or electrical instruments to record nervous reactions. They could wear people down by depriving them of sleep, solitary confinement, or interrogation. But even if they find out what you feel, they still cannot alter it.
Winston and Julia are amazed when O'Brien, an Inner Party member, is able to turn off the telescreen. Despite this privilege, O'Brien remarks that it is still dangerous to leave it turned off for more than half an hour.
O'Brien reveals several very sophisticated strategies that the Brotherhood uses to avoid the surveillance of the Thought Police. No member can recognize more than a few others, and any knowledge must be spread slowly. Members may die, or it may be necessary for them to become different people, with different faces. He tells them it is important to change hiding places frequently.
The Party constantly researches new ways to find out what people are thinking - the scientist is "a mixture of psychologist and inquisitor, studying with extraordinary minuteness the meaning of facial expressions, gestures and tones of voice, and testing the truth-producing effects of drugs, shock therapy, hypnosis, and physical torture." Section 2, Part 9, pg.194
The Government's MK ULTRA already did all of this
In the Ministry of Truth, surveillance of the prisoners is extremely close. There are four telescreens to a cell, one in every wall. The telescreens are very invasive and the voices command the prisoners harshly, making sure, for example, that Winston does not put his hands in his pockets.
Parsons is arrested for thoughtcrime because of his little daughter. She listens at the keyhole, hears him saying, "down with Big Brother" in his sleep and runs to get a patrol. Parsons is actually proud of her for this; he was completely unconscious and unaware of doing anything of the kind, and thinks that it is terrible that he could have unknowingly harbored these evil thoughts. He says that when he goes up against the tribunal he plans to thank them for saving him before it was too late.
The telescreen yells at Winston for covering his face when Parson uses the lavatory pan in their small cell.
Winston realizes that for seven years the Thought Police have watched his every act, word, and thought with far more subtlety than he would ever have imagined. They even replaced the whitish speck of dust on the corner of his diary so that he would not think it had been disturbed. They have soundtracks and photographs of absolutely everything he has done.
What I'm trying to get at is that governments can brainwash citizens, tell them false accusations, squash up risings, and people generally won't committ crimes if they know law enforcement and the government is watch their every move.
How the NSA's Domestic Spying Program Works
Details of Every American’s Call History
First, the government convinced the major telecommunications companies in the US, including AT&T, MCI, and Sprint, to hand over the “call-detail records” of their customers. According to an investigation by USA Today, this included “customers' names, street addresses, and other personal information.” In addition, the government received “detailed records of calls they made—across town or across the country—to family members, co-workers, business contacts and others.”
A person familiar with the matter told USA Today that the agency's goal was "to create a database of every call ever made" within the nation's borders. All of this was done without a warrant or any judicial oversight.
Real Time Access to Phone and Internet Traffic
Second, the same telecommunications companies also allowed the NSA to install sophisticated communications surveillance equipment in secret rooms at key telecommunications facilities around the country. This equipment gave the NSA unfettered access to large streams of domestic and international communications in real time—what amounted to at least 1.7 billion emails a day, according to the Washington Post. The NSA could then data mine and analyze this traffic for suspicious key words, patterns and connections. Again, all of this was done without a warrant in violation of federal law and the Constitution.
The Technology That Made It Possible
In addition to investigative reports by the New York Times and others, AT&T technician turned whistleblower Mark Klein provided EFF with eyewitness testimony and documents describing one such secret room located at AT&T’s Folsom Street facility in San Francisco, California.
It works like this: when you send an email or otherwise use the internet, the data travels from your computer, through telecommunication companies' wires and fiber optics networks, to your intended recipient. To intercept these communications, the government installed devices known as “fiber-optic splitters” in many of the main telecommunication junction points in the United States (like the AT&T facility in San Francisco). These splitters make exact copies of the data passing through them: then, one stream is directed to the government, while the other stream is directed to the intended recipients.
The Klein documents reveal the specific equipment installed at the AT&T facility and the processing power of the equipment within the secret rooms. One type of machine installed is a Narus Semantic Traffic Analyzer, a powerful tool for deep packet inspection. Narus has continually refined their capabilities and—as of the mid-2000s—each Narus machine was capable of analyzing 10 gigabits of IP packets, and 2.5 gigabits of web traffic or email, per second. It is likely even more powerful today. The Narus machine can then reconstruct the information transmitted through the network and forward the communications to a central location for storage and analysis.
In a declaration in our lawsuit, thirty-year NSA veteran William Binney estimates that “NSA installed no few than ten and possibly in excess of twenty intercept centers within the United States.” Binney also estimates NSA has collected “between 15 and 20 trillion” transactions over the past 11 years.
In April 2012, long-time national security author James Bamford reported NSA is spending $2 billion to construct a data center in a remote part of Utah to house the information it has been collecting for the past decade. “Flowing through its servers and routers and stored in near-bottomless databases,” Bamford wrote, “will be all forms of communication, including the complete contents of private emails, cell phone calls, and Google searches, as well as all sorts of personal data trails—parking receipts, travel itineraries, bookstore purchases, and other digital ‘pocket litter.’”
PRISM surveillance program