Originally Posted by merlinextraligh
Essentially yes. If you're descending a hill that's steep enough to spin out a 52x12, in the mid 40's, the power input necessary to raise your speed even 1 mph is high enough that it's not worth the effort in energy expended.
That's not when you need it. When you get to the bottom of your descent and the road starts leveling out then tilting back up, you will still be going at (or near) descent speed, but you want to start inputting more energy to keep your speed up as long as possible on the ascent.
From what I've observed, many (most?) riders simply coast back down to climbing speed, then pile on the power. If you can input energy at part power
before you fall to climbing speed, you'll have a somewhat shorter climb and a smoother and more sustainable power output.
So there is a point to gearing so you can pedal at top speed.