Slipper clutches

[Ghoti]

What does a slipper clutch do exactly?

Neil Spalding (of Sigma and MotoGP commentator fame) explains here http://www.sigmaperformance.com/slipperclutch.html
He owns Sigma Performance so may be a little biased, but I like the way he has written this.

Unless you are down shifting at such high revs that the engine braking may make the rear wheel lock, no real point to them.