keep playing with your profit means you are trying to win against the house in the long run which it's has discussed many times and the result would be you won't make it. better to gamble small amount only if you want to keep playing even you have got profit , so when you lost it all back to zero you wouldn't feel too regret/upset.
Isn't playing gambling games like dice, roulette, slots, playing and trying to win against the house? So basically, when you play even at the beginning you are already playing and trying to win against the house. So I don't see any difference if you keep playing with the profit in here except that, you are just playing with the amount you acquire in winning and saving the initial bank roll. So virtually you are playing the house money against itself to win more money. And losing that amount will mean that you lost nothing.