There are only 2 "poker" reasons to leave. You should also probably leave when your girlfriend shows up in sexy lingerie, but that's obvious.
1) To prevent tilt from hurting your win rate.
2) There are no more easily exploitable players at your table.
Leaving because you've doubled your buy-in is crazy, because that usually means there are bad players at the table and now you can win even more from them when they make mistakes because your stack is double its normal size.
Originally Posted by jazzaxe
When I play full ring, I pick a number of hours I will play. I might stay if I am having a good session and the game is good. (Loose and paying off better hands) A lot of guys will hang in when they are losing and play longer when they are not winning; when they double up they quit and won't continue. I like having a big stack and using it against players; so I won't leave when I double up, especially if it happens early in a session.
Also, some excellent advice there. Limiting the number of hours you play limits how often you tilt. People tend to play their longest sessions when they're losing & tilting.