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.
if you only play with the profit then if you are win in next round, i guess you only get small profit too. i think you need to try to play with your base bet so you can save your profit and if you win, you can collect your profit until you can withdraw it. but maybe you are enjoy to do this and its the best for you when you are playing gambling.