This topic often results in a good discussion -- though can, at times, become contentious because of the ratios that people assign to sprung: unsprung.
I've seen ratios that range from 2:1 to 10:1. I've seen people claim that the reduction of unsprung weight results in HP gains (wrong; but it does free up resources that can be dedicated to rotating mass).
Additionally, there are two things that people talk about when it comes to unsprung weight. One of them, however, should not be dealt with when discussing unsprung weight: acceleration (and braking). Rotational mass is relevant here. Unsprung weight is not.
Meanwhile, unsprung weight is relevant to the discussion of grip -- especially as it pertains to uneven driving surfaces.
If I'm wrong about dividing this discussion into two separate issues, please let me know.
I'm hoping we have a physics geek on the site who has a good understanding of this stuff -- and who can explain it in lay terms.
Discuss.