There is evidence that it reduces transmission somewhat: probably not a lot, but even a few percent will have an impact. The best thing to do, mask or not, is a

There is evidence that it reduces transmission somewhat: probably not a lot, but even a few percent will have an impact. The best thing to do, mask or not, is avoid close contact with other people. Avoid crowds; maintain 2m distance; and so on. The advice has never been about protecting you or anyone else in particular, it is about reducing the transmission in the general population. With that goal in mind, small benefits can have a major impact overall.