With the great big caveat that we don't know what really happened:
"Bearing in mind Russia is on the strategic defensive and Ukraine on the strategic offensive, in the short term it's an advantage to Russia, definitely," said Ben Barry, senior fellow at the International Institute for Strategic Studies.
"It'll help the Russians until the water subsides because it makes it more difficult for Ukraine to do assault river crossings," he said in a phone interview.
The floodtide inundating the region will prevent the use of heavy weaponry such as tanks for at least a month, said Maciej Matysiak, security expert at the Stratpoints Foundation and ex-deputy chief of Polish military counter-intelligence.
Having cited sources, I want to add some more observations/opinions:
Shorter defensive lines are better, for the defender. They can concentrate more troops there, closer to each other, with no risk of outflanking. An extreme case of this would be Thermopylae (Spartans vs Persians). Conversely, the attacker wants to probe around and decide where to commit all his efforts.
Ukraine has been very diligent so far at diversions. No one really could make out what big outcome they were hoping to achieve with all their river crossings near Kherson, but they certainly made sense to annoy the Russians and force them to guard the area. Now, that's gone, at least for a while (see quote above).
If it was done on purpose, whoever did it has an advantage in this action, as they did not plan based on the status quo. Yes, that certainly counts for Ukraine as well, but if Russia did it, then they can expect to have thrown a bit of a spanner in Ukraine's either primary attack, or its diversions. Call it a first mover advantage, if you wish.
The flooding will not last forever and whatever benefits in terms of water crossing difficulties and mud the Russians get will not last forever (see again that quote above about a month). That was literally what Strelkov was quoted about in the matched Q:
create a threat (in a week or two) of crossing the Dnieper in a wide area above Novaya Kakhovka - after a very significant decrease in the level of the reservoir and the same narrowing of the current water barrier.
Yes, but right now the game clock is ticking on the Ukrainian side, with them having gone on the offensive. If they waste some of their time and momentum due to the dam breach than it costs them more now than it will cost the Russians with a shallower Dnipro, once the mud has dried up, if they've managed to hold off Ukrainians until that time.
Some will say that there is more flooding on the left/east side of the river, held by the Russians, thus making it less likely it was them. Well, yes, but asides from their sunk costs in mining and entrenchment, they want as much mud pools as possible between them and the Ukrainians, so that can also be seen as a feature (flooding terrain is a long established defensive practice, used by the Netherlands in WW2 for example).
ISW said it was unsure what happened and that they observed a number of Russian troops having to reposition themselves, so didn't plan well (the loss of those fortifications is a point also made by Strelkov):
Ukrainian Southern Operational Command Spokesperson Natalia Humenyuk stated that Russian forces are having to evacuate their forces on the east (left) bank of the Dnipro River because subsequent flooding has disproportionately impacted the Russian-occupied bank of the river. Footage published on June 6 purports to show Russian forces withdrawing from flooded positions, suggesting that these forces were not prepared for the flooding that resulted from the destruction of the KHPP dam.
Then again, the Russians did make use of it too:
Available footage from June 6, corroborated by claims made by Russian milbloggers, suggests that the flooding washed away Ukrainian positions near the Dnipro shoreline and forced Ukrainian formations to evacuate while under Russian artillery fire.
Keep in mind, this is quite a big escalation in terms of material damage and also in terms of Crimean water supply. While it might mess with fortifications, it is likely that initial planning was done assuming that this dam would not need blowing up. And Russia did from the get go have a fairly deep and comprehensive network of fortifications (standard WW2 Soviet practice, digging in), not all is on the river. Losing some of the waterside ones but with second set available to rely on isn't such a bad deal if Ukraine can't cross.
This BBC article has a good map, dated May 8th, scroll down a bit, it's the first actual map. There are plenty of fortifications inland.
p.s. at the risk of stating the obvious, the dam was a major way to cross the river. That is where the Russians were doing land logistics when their troops were on the West bank, but after the bridges at Kherson had been blown up. They evacuated Kherson just near the time when Ukraine would have the dam and its approaches under artillery range.
IF, and that is a huge IF, Ukraine had managed to seize the dam by surprise, neutralize any explosives, they could have used to get troops across in a way that has no equivalent until hundred of kms up North, near Zaporizhzhia. And certainly way above the potential risk of amphibious crossings of the river. Likely? No. Risky? Yes. But similar things happened in WW2, such as the bridge at Remagen (1945), in 1940 by the Ardennes, 1944 bridges in Normandy. As a potential crossing point on its own, the dam was always a low probability, high impact, risk for Russia. They had to guard the backdoor, now they don't.
p.p.s. At least one expert, Maciej Matysiak cited in first quote, (Polish) thinks Ukraine probably had it in its list of contingencies (and again cites the benefits).
The Russians are trying to protect themselves from the Kherson side, which does not mean that the south is cut off. The Ukrainians certainly expected such a scenario, he noted.
The Dnieper is a significant water obstacle, this only strengthens this obstacle. Certainly, the Ukrainians took this into account, he stressed.
Back to Russia shelling Ukrainian troops withdrawing from water rise. The more I think about it, the more it seems very incidental and more a side effect than a primary decision driver: why would they not do it if they had the opportunity? Remember this breach is a big event, politically, strongly condemned by UN. Just to take potshots at some UA troops, which is std combat behavior? I would be surprised if Ukraine hadn't done exactly the same to those Russian troops vacating their entrenchments. ISW almost never reports/speculates on UA activities before Ukraine acknowledges them - they say so themselves. They're not dishonest about it, they just don't want to help out Russian military planners.
Urrf, this is getting to War and Peace length, bear with me, but I'll summarize a 15 minute YouTube from Anders Nielsen (Danish military analyst, usually a quite insightful guy). He states he is speculating:
it was probably them Russkies wot did it, but...
the dam wouldn't collapse accidentally, nor by artillery, just too big.
it is a RU military gain, in the short term, but that might reverse to a relative UA gain in the midterm (weeks/months) due to reduced Dnipro/lake. As an extra barrier now, sure, it works, but the Dnipro was already such an obstacle that it hardly seems worth it.
the dam's road bridge was unusable by Ukraine (so much for my theory) due to Russia's thorough demolition in Oct/Nov 2022.
Russia would have had much to gain from blowing the dam, if Ukraine had a major operation underway in East Kherson at the time. Maybe to strand/incapacitate troops. Ukraine did not, so it is a one-shot weapon, used at the wrong time.
He concludes Russia probably did it, but likely by accident/miscommunication/bad decision, because it wasn't worth playing this ace card now and not having it as a backup later: mistakenly firing demo charges, high level panic about (small) Dnipro incursions and UA counteroffensive, overreaction/panic by local demolition garrison who might have thought the situation had reached their stated "blow dam if X happens" instructions, etc...