Obviously it's all Euro superstitious nonsense, but I thought the reason that roadies did it the day of the race so that you wasted less energy regrowing hair before the race? Dunno why you're meant to do it the day before a TT, maybe the stubble is more aero?
I've always thought it was bad to do it the day of, or the day before, some balls about your body using strength to heal micro abrasions?