Yes, private pensions have different rules and regulations about when to put money in, take it out, etc. For one thing, social security forces you to contribute. If you would rather spend your money on something else (in general, or just this month), you can't. Sometimes that hurts people who are trying to make rent. Sometimes it's inefficient b/c they could have used the same money for something better. Private pensions, if they get nothing else right, at least are voluntary.