I might be under a mistaken impression, but--in my mind--using a gun isn't about wounding a person (although delivering a coupe de grace is, obviously, inappropriate).
I'm under the impression that if a court can prove that you intentionally shot someone in the leg or the foot, that you can go away for some hard time because...
by your own standards at the time of the shooting...you didn't believe that deadly fotce was warranted. And, of course, if deadly force wasn't warranted...then why did you use a gun?
In other words, you contradict yourself (with some exceptions, because every situation is unique) when you deliberately aim for a person's foot or leg.
So...I always practice to aim for center mass.
I also practice the Mozambique drill, aka "failure to stop" drill that puts two in the chest and one in the head.
May God forbid that I ever have to do this to another human being.