I carry a mask when doing things outdoors, in case for some reason I have to get close to someone. I try to arrange things so that this doesn't happen. I did this pre-pandemic as well though :-)

I can't think of any rational support for me wearing a mask when hiking on the 80 miles of empty trails on the mountain I live on. I mean, when the weather is bad, I wear something over my face to avoid freezing, but that's a different issue.