@Cucoo
Aside from being weak it can free a pokemon from trapping moves like Sand Tomb, Whirlpool, Wrap, Bind, and others. Those moves do low damage themselves, but when used will trap an opponent preventing them from switching out or running away as well as dealing low damage over time. Rapid Spin deals damage and can free you from those moves. Quite useful actually.
In fact...
Rapid Spin:
http://bulbapedia.bulbagarden.net/wiki/Rapid_Spin_(move)