there is none, it is purely cosmetic / organizational.
if you use player roles, then the overall rating score you use, is based on the listed position. so for folks who use player roles, there is more incentive to change positions of players.
in theory, you could make all your PGs centers, and vice versa, and be annoying to game plan against, but this is generally sort of considered a dick move, and i haven't seen it out in the wild. that's really the only thing anyone has come up in terms of an actual advantage, and its a pretty sketchy one at that.