This would be great, very realistic. Most accounts I have read of medieval battles like Towton suggest that repeated bouts of 'combat>fall back and rest> combat' was the way medieval battles went, not the 'stand your ground slaughter' that most MTW battles result in.
of course, as you say, you can also finally pull off 'engage and retreat traps' on enemies to lure them into an encirclement. it would make close-in skirmishing and rearguard actions more effective too. It would be more realistic for it only to be made available to well-trained or elite units though, ones with good discipline.