For me it was no longer having to live in such a bad atmosphere anymore. My dad was a really difficult man to live with, and in the last year I lived there it was just awful. I also had to look after my siblings a lot and my parents always put them first.
Another thing is I wasn't allowed to eat/wash/make noise after about 8 o clock. Even now (15 years later) I love being able to stay up as late as I want, have a bath when I want etc.