I personally never grind my weed, UNLESS it's really fuckin shitty, with mad stems and shit. Then it's just easier to clean it.
Normally I like to take my time, and pinch off little bits here and there when packing. I can't see how grinding good weed up in advance would make it better. Course, I'm one of those slooow stoners. When I get weed I like to stare at it for awhile...I think the crystals are pretty. *shrug*
But whatever, to each his own.