Much depends on one's goal for the day.
For the soldier, field cop or guard - - Anyone whose duties entail seeking out the enemy, it makes a lot of sense to carry all the armament and reloads one conveniently can. Likewise, if going afield, into the woods, mountains, or desert, resupply may be a long walk away.
For most of us, in town, a LOT of spare armament is rather unrealistic, and perhaps a bit pugnacious. The real purpose of the reloads is to be able to regroup and return to ready status following a brief, violent, encounter. Lightning DOES strike twice on the same day, though the statistical probablility is vanishingly small.
I'm an administrative staff deputy with a medium-size sheriff's office and I carry a single spare .45 mag. When going out on warrants or with the patrol deputies, I drop an extra mag in my pocket, sure, but we're hunting for trouble. (There's probably a .223 handy, as well . . . .)
On rare occasion, though, the second magazine DOES help balance the off-side of a shoulder rig.
And, all the above being said, I've been known to carry a second handgun.
Best,
Johnny
