I think it would have a more profound effect on mounted archers, particularly enemy ones as the AI doesn't seem to take advantage of the archer's blind spot.
If you're up against mounted archers like the khergit or steppe, you can maneouvre round so that you're on their right, and they'll be unable to touch you unless they swiitch to melee. If, however, there were one among them who turned out to be left handed, you could be in for a nasty surprise.
It'd also mean that the left handed one would probably peel off to your right while his friends went to the left, and so they'd be quite an effective force if you don't pre-empt them.