I frequently wear a full beard but shave it off about a month before a race. Not because it’s any faster (maybe it is, I don’t know), but because I recall reading somewhere that the US Army did a small study where they found that soldiers who had facial hair were much more likely to get sick than those who were clean shaven.
I don’t have a link, and I’m sure if I did the study wouldn’t hold water with most around here, but I always figured if it would the reduce the chance of me getting the flu or a cold a month out from a race, why not.