I hate walking downhill in mountain boots, especially in the summer. On a climb like the Borah NF, I would start up the trail in the Nepals but carry the lightest pair of running shoes possible in my pack. At the first sign of discomfort (either up or down), I change into the runners. Usually this happens after the climb on the descent. Approach shoes are generally heavier and don't smash as flat as runners. The light shoes rarely come out of the pack unless my feet are screaming.