My goal is to hit him with the first round. Wolves travel in packs and what says they haven't decided to shoot it out with you? Ideally, you'll be involved in a shooting (and I hope no one here ever is), in which you shoot the attacker, he stops attacking, you run away, call the police and continue on with your life. But what happens if you actually get into a gunfight, what if there are multiple assailants?
What happens if that priceless, unjamable, fantastic plastic jams? What if you get a heaven forbid double feed and have to rip the magazine out of it, what's faster, getting a new magazine or trying to reassemble your magazine?
Anyone here ever have the baseplate of a 1911 magazine rip off? I have...guess what, it's a fancy single shot pistol, then, because all your extra 7 or 8 flawless rounds are lying on the ground, along with your mag spring and follower. It's cool though, because you can knock out three opponents with one round right?
I'm not saying you should carry five magazines, if you don't that's fine. I do, because I've shot enough to know failures happen and they happen when you don't want them to. I've dropped speed loaders while reloading and magazines too, it is still faster to grab a new one then try and retrieve the grounded one.
Once again, just my opinion and what I do. I would advocate you carry at least ONE spare, and hopefully TWO. Three, four, or five is purely a personal comfort thing.