I've found that granny-gearing up mountains for me hurts my knees. I have to have some push, or my knee (right one) really starts hurting. This, mind you, is on very long climbs like Skyline Drive in Virginia--it's like a 50-mile climb.

But for normal rides, yes, spinning is good, but not empty spinning. I've evolved over the years and I find myself in my big ring more often than I used to be. But I still don't mash.