Professional players always optimise everything for maximum performance. That's why they clip nails at least once a day and buff them every hour (except during a match). As I'm sure you've noticed, they also remove all body hair to reduce air resistance. Hair on the head is left, as it creates a "spoiler" effect that generates more down-force during a jump smash.
It probably varies... of course there are players with facial hair, etc. I feel like once a week is okay but I'm eager to see if people have experience with this, lol.
