I would say that i practice mainly for fun and it is a great way of excersize. There may be better ways of excersizing, but none that i would have fun with. I really enjoy the martial arts, and i think that if you have an excersize routine that you actually enjoy then the excersize will pay off more because you won't make excuses not to workout. Also, for self-preservation - i rely on God for that. There is always someone who can beat you down in a real fight. There is no one who can defeat God. So, my best bet is to trust in Him.