I think we have decades of proof from Asian countries during flu season that wearing a mask does, in fact, reduce the spread of viruses.
I don't think me being the only person wearing a mask in a room full of mouth-breathers does much to protect me, no. But I do believe that it helps rob the velocity and stops the larger droplets of moisture from getting released into the air, helping to reduce the spread.
Is it a 100% solution? No. Almost nothing is. But with the Delta variant infecting roughly 9 additional people for every person that gets it, I'll take all the help I can get.