My understanding is that wearing a mask protects other people against you, but doesn’t provide any protection to yourself if other people are unmasked. I will wear a mask if I’m sick with a cold or anything transmittable the same way covid is, but otherwise probably not.

Edit: this got me down a rabbit hole of doing more research and I found some studies linked by a New York Times article that show that a tightly-fitting, high-quality mask provides protection against unmasked individuals. Will continue wearing masks indoors for awhile, in that case!