Why do special forces get a shaving exemption?

[RockRaven]

4. To leave open the possibility of blending in, where people are not clean-shaven, for one.

Facial hair grows fast, but not fast enough to generate it on demand as the situation requires. The reverse direction (shaving) is the quick one if the situation demanded it.

To eliminate an avoidable source of infection/injury when sanitation is less than pristine as may often be the case in the field (clean treated water for bathing/shaving not expected to be available always).

To obscure facial features from foes and any cameras to reduce identification potential.

To allow identification as special boys amongst friends and allies.

I'm sure there are others.