I do it for the ability to limit risk, and one feature that really makes it nice: it adds on to your position when it's winning, and subtracts from a losing position.
Which means: gamma increases/decreases your delta as the price moves towards/away from your position, automatically increasing your exposure. Keeps you from making the mistake of not adding to a screaming winner.
Also have been learning, gradually, the art of trading IC's, which puts you short gamma, which is a scary thing. The returns have been impressive so far (but I've been using a different distribution than the standard-issue Gaussian to set the strikes; the probabilities are different and, based on historical results, far more realistic), but I know there's a surprise waiting around the corner for me.
So, at this point, I'm mostly trying to figure out the best way of hedging against extreme moves. From what I can see, only experience (which of course will mean having to lose some money along the way) will tell me for real. Everyone seems to have a different method.