I always do this. If I made a profit with my deposit I only play with the profit. This the way I like to play most of the time.
By doing this I know I am not going to lose a lot of money because I only make one deposit each time I play.
Everyone has different method but for me I don't consider it as a profit yet if I'm still playing. I can only tell that for a day I'm profitable when I stop gambling and withdrew with a profit. I have a target to get and once I hit it already, I automatically stop and I'm able to follow my game plan for years already.
although it is a fact that most of the people cannot make money from gambling, as gambling is a game of luck and no one can be so much luck to make money from gambling. but still there are some people who know the thick and think in gambling and can therefore make good profit from it. they have good experience in gambling. they may have good luck also.