It's not a good idea to share a blade razor if you're worried about disease, but in general, shaving can reduce the buildup of bacteria around your mouth. Hair tends to get dirty quickly, and shaving reduces the number of places that microorganisms can live.
If you're trying to find an excuse to NOT shave and looking at health reasons, sorry, that one doesn't work. But if you are able to keep your beard clean and trimmed you can reduce the potential of building up an unhygienic condition in your beard.