Do you mean “turning” as in changing your direction on a battlemap? It seems like facing would be a factor during combat, such that, if you’re facing away from an opponent you’re likely at disadvantage to attack and/or they have advantage in attacking you (or whatever the bonus/penalty may be). I’m not sure how I’d handle the actual turning bit, if turning 180 degrees would constitute 1 full movement, and anything less than that can be done for free (or if all of it would be a free movement).
I generally like the idea, as anything that gives fighters more options and makes positioning important is great. I wonder though if Turning would need to be added as a reaction movement, since you could easily have a melee fighter just move to their opponent’s backside every turn to get an uncontested attack at advantage? So by making turning into a reaction, it gives the opponent a chance to respond, or gives at least gives them a decision on whether to use up their reaction for that or something else. I could see it making combat feel a bit more like a dance or a struggle to gain the upper-hand, which could be interesting for martial folks.