Beards and Hair

Beth asked, so I'll give my 0.02:

One reason for shaving is a discipline issue. Keeping yourself in 
shape and clean looking is supposed to show good discipline (to I buy 
that? Hmm.....). Another reason is you look good for inspections 
(which they even did in the field - I remember Grandad telling me 
about having to shine up and get cleaned up while in the trenchlines 
in WW1 because the King was going to drive by and they had to all be 
out in their best, cleaned up, at attention - the sod didn't even 
look out.....). Another modern reason is many gas masks don't make 
accomodations for them. (Makes it hard to get a seal). Said masks 
often don't make good allowance for spectacles either (I hate the 
Army issue combat spectacles) and wearing contacts in a chem-bio (or 
even very dirty) environment is anathema. 

Hair, they keep to specified lengths (unless you're in the Navy, 
seemingly, who can get permission for beards) because in the field 
(as a grunt), you need some hair (I think 1/4" was the minimum) to 
protect from sunstroke/burn and you want little of it because it is 
often hot and therefore more hair equals more chance of heat related 
distress. And hair (beard or cranial) is an ideal living place for 
all manner of lovely little biting contagious vermin.

So there are practical reasons for the limitations on hair length, 
but their is also the military culture of "sameness" that plays a 
role. If everyone looks like a buzzcutt, identically uniformed little 
grunt, it makes it a bit easier to depersonalize them, treat them 
like expendable resources, and order them to do things that will kill 
them. 

Or at least this is some of the comments I've seen or read over the 
years and some of my own experience in the infantry.

Tomb.