It's really interesting to see the myriad of opinions on when to pull your gun (why this has focused on when to shoot is beyond me, as that was not the OP's query). I think the majority of the good people on this board share my sentiment that I have absolutely ZERO desire in my life to have to pull a gun, much less shoot someone. Talk about shooting to kill? When the Chinese invade our country, I'll shoot to kill. Until then, I only have interest in killing paper. You should only pull your gun as a last resort, and like many posters have also chimed in, you should only pull when you have to shoot.
My first resort would be to try and talk the guy down. I would also try to disarm IF POSSIBLE. I would try to get HIS gun, not pull mine. Remember, we can't hypothesize what kind of situation you will be in and what options you may have available to you. You just *know* when you're on the short end of the stick. Training will help you better assess your situation (or at least thinking about possible scenarios) when the chips are down, and you will have to sort through a variety of outcomes with a moment's notice.
In most cases, it's probably best to give them what they want. I'm not a rich man and I work hard for my money, so taking even a few hundred bucks out of my pocket is not something that would sit well with me. I'm not pulling a gun, but I'm not giving you my wallet either. I have been held up before and insisted that I had no money (I did) until he got really frustrated with me and walked away. People who rob here actually jump people (Chicago) and brick you in the back of the head. This requires one decoy, and one to flank. This has happened to many friends of mine. They don't need a gun for this, but they get your money every time.
"Shut up, crime!"