For me it was how much it forced me to become an adult. I first lived on my own when I was 21. I could tell a big difference between me and my friends who lived with roommates in terms of maturity.

There were other circumstances the probably led to this as well, I was in the military and living over seas(Spain). However, just living on your own forces you to manage a whole new level of responsibilities living at home or with roommates does not.