I do that because I'm short and the seats are so deep that my knees fold before the end of the seat, preventing my lower back from resting comfortably on the back of the chair. You might try a chair where you can rest your feet somehow so that you can be comfortable. My solution was to get a tilting foot rest to put under my desk. It works, but I still sometimes want to sit the same way because I turn around in my chair and have the same problem.