Yeah, play with your profits will be safe for you to keep your capital safe. If you lose you will just lose your profits not your main assets.
But would not it be better if you saved some of your profit and used some of it for another bet? Because if it is, even if you lose you still get some of your profit, and if you're lucky you will add to your profit. Gambling can give you a profit, so if you win, why do not you keep some?