http://en.wikipedia.org/wiki/Dementia_pugilistica
Effects that we thought would only manifest from concussions actually manifest from multiple blows to the head too. Boxing, MMA, American Football, are places where medical research has made a great deal of progress in determining the effects of brain injury from hits to the head over a period of time.
That being said, it will help you with self-defense and workout. If your goal is purely self defense, Krav Maga might be a better route, as it focuses more on practical defensive application and has plenty of weapon defense training.