can somebody 'splain to me the strategies for "liberating" roulette chips? I've heard the basic..."buy in, play a little while, make a last bet and leave while the ball is spinning with a chip in your hand"

Why anyone who has a bet down would want to leave the roulette table while the ball is still spinning is a mystery to me! What happens if your number comes up? Would it not be better to cash in your pile and then take a hike??