In Risk from what I remember you could always choose how many armies you wanted to attack/defend with. I don't remember that helping any. However if you could use 4 die instead of 3 and 3 instead of 2 perhaps you might want to allow the person how much he wants to use.
Actually, I also remember, wasn't there something like... whatever you used to attack with you have to move into the conquered territory? So if you roll 3 die you have to move at least 3 troops? Man, maybe I messed up the rules...
Tyler, yeah you did mess rules a little there. In Risk you can choose the amount of armies you can attack with, but that's not the request.
At the moment it's a MAXimum of 3 vs 2 dice. The new version of Risk introduces two more, so now it's a maximum of 4 vs 3.