I notice I use my glutes more while climbing. I imagine using my hips to push my legs down while out of the saddle. For me, it's a good way to alternate the muscles I'm using while on a long climb. I'll sit and spin for a good while, get out of the saddle for a bit, sit for a while again, then stand and use hips and stomach obliques (almost like you're "dancing on the pedals"). Rinse, repeat. This way, I have 3 or 4 muscle groups I can alternate between instead of just "sit or stand".

YMMV.