I use mine when at a trail junction to determine which trail for dead sure - I usually have a good head for knowing what direction I'm going, but I don't feel like wasting time backtracking so will verify, because I've been known to be wrong, particularly in a forested area without major landmarks. Not all junctions have the signs that provide every destination on the sign, and state parks in particular can be bad about that.

i use the compass to get a bearing and the map to determine how I actually want to travel vs. going straight on a bearing.

I use the compass to show others how to use it.

I've used it to verify the gps - nope, don't trust 'em, with good reasons. I'm actually faster with an interpolator and compass than other folks on my team are with their gps units.

We're expected to double check all the time with a compass for SAR. Last training we failed to do this religiously and someone led us a merry roundabout course using - attempting to anyway - their gps.