Sprung weight vs unsprung weight.

My understanding is that the springs themselves count as sprung weight?
This was my next question.
I remember reading about this in a chassis book a long time ago.
Next part of this question...is unsprung weight seen the same as sprung weight? Perhaps that is not the best way to put it. In the book I was reading the author was emphasizing how losing 10 pounds of unsprung weight is the equivalent of losing 100 pounds of sprung weight performance wise. Didn't make much sense to me back then...still doesn't now. Might have actually seen it in a wheel catalog...or perhaps it was an old Wilwood catalog. Sounded like a bit of a sales pitch but...
Anybody know if this is actually factual or just some sort of claim to try and get folks to spend their hard earned $$ on a certain brand of products?