The other side of the argument is that it makes fighters fight smart.   No longer can they wade into untold hordes without really worrying about  being hurt, spreading death and mayhem in their path.  I'm thinking of  the scene in LotR:  TTT where Aragorn and Gimly jump off the battlements  at Helm's Deep onto the bridge into a sea of orcs and goblins.
 
A rule like this wouldn't be one for the super heroic games who want to  emulate that scene.  But, for the  GMs who see that scene and say,  "Riiighht.  Not in my game," this rule might be useful.
 
Instead of just wading in, fighting one-on-one (or one-on-nine), and  doing the deed, this rule would make a fighter's player think more  strategically and tactically.
 
Instead of, "Hey!  There's 12 Orcs!  Let's go fight 'em!", the rule  would encourage a player to think more along the lines of, "Hey!   There's 12 Orcs!  I'll get their attention and draw them back here.  You  two spring an amush from the sides, and we'll catch 'em by surprise."