Question about drawing on a drawn gun

So in doing my research leading up to taking my CCW class, one of the sort of "rules" I came across was that you should never draw on someone who already has a gun drawn. Well I went to take the CCW class a couple weeks ago, which was great, but the instructor was giving examples of encounters where you might have to shoot from the hip (which he was instructing us on doing). One of those situations was being robbed where the robber would pull a gun out and demand your wallet/money/whatever. In the example the instructor said he would feign compliance (hands up, slowly reach toward wallet, etc) and would then draw, take a step to the side, and shoot from the hip. I didn't think about it at the time but this seems to be counter to what many people say. I was wondering what the opinions of you all are on this topic. Is it ever recommended to draw in this situation or should you pretty much always just hand your stuff over and hope that the guy doesn't shoot you? via /r/CCW http://ift.tt/2amikiK