Here in Denmark we pretty much have "forced" retirement saving. Almost everybody in regular employment pays about $15 a month plus 12% of their monthly salary into a pension fund. 
You can save more on the side, but not less.
Why would a country do this?
I think there are two major drawbacks to this.
People have different tastes and needs. Some people might want to spend more money now, while others may be aiming for a much more uniform distribution of income. Why prevent people from living according to their tastes and needs?
Risk is a factor. The return from the investments may change due to economic factors, the retirement age and tax rules may change due to political factors, and so on and so forth. Most people work from their 20s until retirement in their 60s and 70s. That's a period of 40-50 years, over which so much can change, so taking away people's income now and promising them you'll pay them back so many decades later is a promise with too much variability and risk involved, and people have different risk aversions. The forced retirement system ignores this risk aversion and pretends every population member is identical.
What are the pros?
 To be precise, you only pay 4% of your salary into the pension fund, and your employer pays the remaining 8%, but it's still kind of the same thing, because we could imagine the employer could just give me those 8% as a salary instead of putting it in my pension fund.