Mike Dimin, explained it this way back awhile ago in a post.
Quote:
The pup height is probably the least critical adjustment on your bass. If you intentionally misadjust the pups all the way through their range, the only place that you'll usually find a problem is at each end of the adjustment range.
At the Very lowest setting (max gap between pup and string) you will notice a lowering of the output to the amp. At the very highest setting (minimum gap) you will notice something called magnetic choking. This is caused by the magnetic coupling to the string, actually acting as a magnetic brake that will dampen the sustain.
Play around with it. You can't hurt anything. On the other hand, you aren't likely to improve anything either.
Hope this helps!
Treena
__________________ Personal opinions are totally subjective.