Actually the \"size\" does have gameplay aspect as the larger the mini the longer reach it has. generally speaking anything medium size or smaller has no reach, IE they can only attack adjacent squares. Creatures large or bigger start to have a longer reach allowing them to attack farther squares. Such as large monsters tend to have a 10 foot reach, so 2 squares. Of course reach is father adjusted by the monster, just as differant medium sized weapons, like polearms and spiked chains, change the reach for attacks.