In our military unit, our orders were "shoot to kill." Not wound, not maim, not "to stop the threat," but to kill.
In our federal law enforcement agency, we were taught and trained to "shoot to neutralize the threat." That sounds much nicer in a courtroom and more pleasing to the folks who are typically afraid of their own shadow.
Either way, military or civilian, the result of your shooting someone is typically the same.
Having smelled way more gunsmoke than I ever would've cared to, I'll NEVER advocate having a "pre-planned" number of shots you'll fire, shot placement, etc.
Every situation is different. I speak from firsthand experience. In some situations, your gun is not the first one out and firing and you're damn lucky to hit the bad guy ANYWHERE with ANY NUMBER of rounds. Other times, you may be in complete control, but the person(s) facing you down decide to become suicidal idiots--obviously shot placement is factor number one.
And then there are the situations of is it one bad guy or four bad guys who are trying to do you harm? If you've trained to mozambique every time you see a human silouhette and you're carrying a six-gun when four guys attack, you have a bit of a dilemma on your hands.
Don't laugh. I've seen it happen with some cops and agencies that train one way and one way only.
My advice, in a civilian situation, would not be to "fire until the threat is no longer a threat." My advice would be to fire until you can safely haul ass to a safe location.
If every single gun owner belonged to the NRA as well as their respective state rifle/gun association, we wouldn't be in the mess we're in today.
So to those of you who are members of neither, thanks for nothing.