I've been, for the first time, teaching fairly regularly in my martial art. In fact, once we move to Elsewhere, I plan to open up a school. This, of course, is a rather involved undertaking; I need to know how to teach well, among other things. Thus, practice.
One reason for teaching is the desire to give something back, to the art or to one's own teacher. It's a sentiment I certainly share. But I'm also finding that there are great benefits for me, even though, of course, the students benefit more.
As I try to demonstrate the techniques, I find that I need to clarify them for myself as well. If I don't know exactly where the sidekick prepare is, I won't be able to show a student. And if I don't know why it's there, they won't be able to remember it. Nothing aids memory like knowing the reason behind something.
So as I lead them through the basic techniques (which, supposedly, I have down cold), I find myself re-learning and deepening my knowledge of those same basic techniques--I'm becoming a better martial artist, and better student, through teaching.
And watching others make mistakes and learning how to correct those mistakes allows me to generalize knowledge that was in danger of becoming specific to my body. If I only know how the technique looks and feels to me, I don't really know the technique, which after all is available to anyone with the requisite physical ability. It's all pleasantly philosophical that way.