Well TBH most of the time i leave when there is no more money left. But only in small sums like 20$ or so if i go over 100 i cash half and play half.
So am I, although I feel regretful everytime I am already up at some point and then suddenly I get cocky and in no time, I bust everything and end up cursing myself. But nowadays, I assure myself that I should leave the game before I start getting the feeling that I am the luckiest man in the world.