He'd use in his shield animation just not to block arrows, like Link in Smash bros 64 and as I said it would power up the Falchion in his attack. It would please basically everyone who'd played Fire Emblem 3 as it's an enormous part of the game, and no one except you seems to have a problem with it.
For those who haven't played, heres an example of its importance. MASSIVE SPOILERS
http://www.youtube.com/watch?v=dI0mGVYVv1A
People who play Fire Emblem DS will start wonder why the shield is absent and in the Smash bros Series if it stays absent for the next installment. Honestly why are you so opposed to the shield? Marth looks awesome with the thing, and it really goes with the Falchion. It would be an awesome addition and with no minuses. You are basically the only person so vehemently opposed to it.