I always carry a spare mag for my Glock 26, though usually in a pocket rather than on my belt. My pistol might malfunction. The mag might get knocked out of my gun in a fight. I might run out of ammo and need to reload.
I have to dispute Leadcounsel's statements:
"A) you're a really really bad aim, in which case you need more practice"
Skill degradation in gunfights versus "practice" has been estimated by many authorities to be in the 50%-80% range. This means that even a well-practiced shooter who scores 100% on a qualification course may only shoot half that well when under deadly stress.
"B) you are severely outnumbered and have no business drawing your gun, you should leave the situation immediately
"C) you are severly outnumbered and should draw your gun and leave the area immediately"
If I am severely outnumbered, I am MORE likely to need my gun (and maybe a spare mag), not less. Obviously, if one can safely withdraw from a situation, one should, but this applies equally to situations where one faces a hostile individual or a gang.
I also find this "I can hear the DA now" stuff pretty amusing coming from the guy who, in another thread, says that he:
* wears a threat level IIA vest regularly (I can hear the DA now, asking why a mere citizen needs body armor like that used by police)
* uses a Glock 35 .40 with a 15 rd clip (I can hear the DA now, asking why a mere citizen needs a high-capacity pistol firing high-powered police rounds)
* suits up with pistol, flashlight, phone, vest and electronic ear protectors when there's a noise in the house (I can hear the DA now, asking why a mere citizen needs to outfit himself like SWAT cop to confront a teenage burglar)
* uses hollowpoint Corbons (I can hear the DA now, asking why regular or police-issue bullets weren't deadly enough for this mere citizen)
My point is that this fear of hearing what a politically-motivated prosecutor MAY say to a jury seems pretty silly. I am willing to bet that neither Mas Ayoob nor Leadcounsel can produce a case where a defender was convicted in an otherwise righteous shooting simply because he was carrying a spare magazine.
Recycled scare stories about courtroom theatrics from anti-gun DAs helps fill Massad's monthly columns, and probably sells issues of "Combat Handguns" to lots of petrified, underconfident new shooters. I'm not sure they should materially affect the choices of serious gun carriers, whether the issue is carrying spare magazines, wearing body armor, or anything else.
I am a leaf on the wind.