Well, here's the way I look at it.
Just because you draw the weapon doesn't mean you have to 'use' it. But you shouldn't draw the weapon unless you are prepared to use it, think you need to use it, feel you are morally justified to use it, and preferably you also feel your are legally justified to use it.
I think some people get confused by statements like if you draw it you better use it, because I think what some people mean by that is that you shouldn't draw your weapon unless you are capable and willing to use it, because if you draw your weapon with no intention to ever shoot someone, that's a pretty good way to get killed, because now you've elevated your perceived threat to your attacker, who will now potentially take even more aggressive and dangerous action towards you, either with their own weapons or with yours, so by drawing a weapon you don't intend to use, you're elevating your own risk.
However, while you should be willing and capable of using any weapon you draw, that doesn't mean you have to use it to its full capacity. For example, where do you draw the line of 'using' it. In some cases you may only need to draw it, sometimes you may have to shoot it, sometimes you might have to empty the magazine, reload and repeat. Saying that you need to 'use' the weapon, i.e. shoot it, every time you draw it, is about as ridiculous as saying if you felt you had to draw the weapon, then you better 'use' everything you had on you, so if that means you have a 15 round magazine in the gun, and two spares, you better shoot all 45 rounds if you feel you 'had' to draw your weapon. There's no rule that says you have to shoot 1 bullet, let alone 45, just because you drew your weapon.
Doesn't everyone say that you use the weapon to stop the threat, no more, no less, right? Like if you are under attack, you're supposed to take appropriate action (flee, take cover, draw, shoot, or some combination thereof) until the threat is stopped. If that means you have to put 10 rounds in a giant crackhead wearing body armor & armed w/ an ak 47, or 3 rounds in a burglar w/ a handgun and no body armor, 1 round that immobilizes and disarms another attacker, or by presenting the weapon to somoene who posed a previous threat to you and yours, that upon seeing the weapon decides himself to flee, in all of those cases, you 'stopped the threat' right?
To me, it's a matter of whether you were justified to use deadly force, not whether or not you had to kill someone. If showing the weapon stops the deadly threat, shooting (but not killing) stops the threat, or killing the attacker stops the threat, it seems to me you are supposed to take the minimum amount of action that is necessary to stop the threat. Sometimes things happen so quickly, and you don't know the ultimate consequence of your actions, like one round may or may not stop them, 3 rounds may or may not stop them, depending on their position, your position, what they appear to armed with, how fast they're advancing on you, etc., these are all variables that will determine how fast you have to take action, and decide to stop taking action and reevaluate, w/ the err on the side of caution for you and yours. But at whatever rate you are able to defend yourself and evaluate the then current imposed threat to you, you should take reasonable efforts to stop the threat, and then stop taking action.
So if you stop the one and only threat, and they are no longer armed or in a position to hurt you, then that's pretty much it, call the cops, hold them there, or get the hell out of there, as the case may be, whether that meant you only had to draw, shoot, or go ballistic, the threat was big enough to you and yours to warrant you begin the process to defend yourself, and the moment there is no longer a threat, you have accomplished your intended goal, regardless of how much 'force' was actually necessary to do so.
As for the point in which you are morally justified to begin the process to defend yourself, and be prepared to take potentially deadly action, that's between you and your maker. Likewise that point where you're legally justified to do so, is in local, state, fed law, and you and your lawyer's interpretation of it. While you may want to pay attention to laws associated with brandishing, etc., at the end of the day, I think if you know when you're legally allowed to shoot someone, then in *most* cases you'd also be allowed to pull the weapon, but not *have* to shoot.
Take an extreme example, clear cut, guy has a gun, says he's gonna kill you, points the gun at you, you pull a weapon and for whatever reason (maybe his gun isn't actually loaded and he knows he's up a creek), he runs around the corner before you get a shot off. You were under a deadly threat, you drew the weapon, but didn't have a chance to shoot because the threat ran away. What are you supposed to do, shoot some shots in the air now, or chase him around the corner and try to shoot him while he's fleeing? No, of course not, you stopped the threat without shooting at all. I don't see how any judge or jury could say that's not a reasonable action.
The question becomes were you justified to use deadly force if you had to based on your laws in that area, not whether you had to actually fire or kill, etc. IMO (I am not a lawyer, and I refuse to use the acronym IANAL for obvious reasons...lol)
Karz