There might be a difference.
If you find the need to make a head shot to stop a threat, for whatever reason, you best be aware ahead of time that you are, in all likely hood making a kill shot.
I, myself, want to be aware of that long before I have to make that shot and resolve any "issues" I have making a kill shot when necessary.
No one needs to any self doubts as they prepare for that shot. No "OMG I'm about to kill someone" should occur. Not that it will be any easier on you, just that it will be quicker and surer.