Guns are like parachutes...
...always carry one more than you think you'll need.
I usually don't need any gun, so I usually carry one. In my placid life, I don't usually worry about reloads or back-ups...
I think it also depends on your weapon. With a high-capacity weapon, I think reloading is less of a priority, whereas with a revolver or single-stack, a reload is a good idea.
I guess it's kind of apples-and-oranges, though. There are more reasons to carry a BUG than just the "New York Reload": Retention, mechanical failure and weak-hand draw come to mind.
The flip side is, do you want to suit up like Batman every time you walk out the door: Gun, ammo, BUG, cuffs, pepper, flashlight, knife, phone, badge, etc...