If you are clean-shaven when wearing tight-fitting masks (ie those which rely on a good seal to the face), this will help prevent leakage of contaminated air around the edges of the mask and into your lungs. You will therefore be breathing in clean air, which will help you stay healthy.
If there are good reasons for having a beard (e.g., for religious reasons), alternative forms of RPE that do not rely on a tight fit to the face are available.