Welcome to WebmasterWorld Guest from 126.96.36.199
Nofollow does not give any pagerank benefit. If you have several links on a page then, roughly speaking, the "link juice" will be divided equally without regard to any nofollows. The share due to any nofollow links is just thrown away and is no longer divided between the followed links.
So, unless there is an explicit desire to keep the googlebot away from the target page, nofollow just wastes a few bytes of bandwith on every page view.