I can see firing a warning shot. If I feared for my life, I wouldn't hesitate to pull a gun if I had one (or use any means at my disposal). If I pull a gun, it's because I have the capacity to pull the trigger if I need to. But the key part is, if I need to. I don't WANT to shoot someone. I don't WANT to kill someone. I don't want them to force me to defend myself in such a way. So I can see brandishing the weapon in the hopes that the aggressor will walk away. All I need to do is make them believe I am willing to use it if they persist in threatening my life. I would personally rather they desist in threatening me and walk away than have to kill them to make them do so.