One thing we need to do as FI's is to make sure that our students aren't scared by operating the aircraft.
I've always found slow flight to be a great way to teach handling ability and to breed confidence whilst demonstrating that the machine won't just fall out of the air when the speed is lower then normal cruise.
I don't just use speed conbtrol in a single lesson. I bring it in at all sorts of points, so people don't just use the "standard" power setting all the times without thought. That way they actually get an understanding of how the machine behaves and the difference between individual a/c.
Some good stuff on here, but there really is no need to complicate matters. As long as we get across the ability to fly the aircraft at slow speeds safely and what is actually happening, then job done. When, where and how is irrelevant really.