Originally Posted by
chaadster
Hmm...I giess I like to drive from "on top of the pedals", so I slide forward a bit when the road tips up steeply to keep both my position the same (body x power stroke) and to keep weight forward. That way, I can load all my weight onto the peak power phase (12-4) of the crank without needing to fully stand, just lifting off the saddle a bit. I think that's how it works, anyway!
Typically, when climbing seated, sliding back on the saddle is more beneficial to sliding forward. As you move back, you better engage your glutes and hamstrings. Thus, you are bringing in muscles that aren't used as much when riding on the flats. It helps save your quads for once you are done climbing.
Sliding forward, or being on the rivet, generally allows you to gain more power while maintaining a low profile. But aerodynamics are less of a concern when climbing.