I think facing is unrealistic in any system where rounds > 1 second. Turning around doesn't take that long.
I checked yes-or-no, but really that's yes more often than no.
I like the tactical element of facing in combat; for example, I would send a henchman or man-at-arms to attack an armored foe's shield side while my character would attack on the non-shield side - if the opponent turned to present my character with his shield, the henchman or man-at-arms gained a bonus to attack the foe's flank.
Turning may be easy, but effectively defending yourself in all directions isn't.