grinding weed for a bowl makes it burn way faster, it is true that you get just about the same ammount of smoke either way, but i'm sure you lose a little bit more with grinded....

as a strict and i mean strict personal rule, i never grind unless i'm about to roll a joint.. i don't even really grind my weed when i roll a blunt, since blunts are a bit more workable, i just make sure the weed is in peices about the size of bb's and there are no stems in it. for a bowl, i just pull off a peice of bud that will fit perfectly snug in my bowl and break it into 4 or 5 peices.

and test this for yourself, grind a bowls worth the weed, take note of how many hits the bowl gives before it's offically cashed, then trying to keep everything the same (the ammount of time you leave the lighter on it, the size of the pulls ect...) but this time, just break a bowls worth of the weed into 4-6 small sized peices.