I carry a BUG 90% of the time, and 100% of the time that I can get away with it.
Its not a matter of NEEDING two guns, its a matter of NEEDING one gun and being able to access at least one regardless of the situation.
Ex. 1 - When I'm driving, I wear my seatbelt. When I wear my seatbelt, I can't draw a gun that is on my hip.
Ex. 2 - When its cold outside I wear 3-4 layers. When I wear 3-4 layers I can't quickly, consistently, and reliably access a gun that is on my hip. A snubbie in a coat pocket or in a pants pocket can be carried with my hand already on it if I want, and it can be out in almost no time. If "almost" isn't fast enough, I could even shoot through my coat.
I'm convinced that successfully defending yourself with a gun has little to do with caliber and capacity. It has more to do with having a gun out and ready ASAP. Milliseconds count more than millimeters.
On that note, I've taken to carrying my 1911 as a "BUG" while the snubbie or Kahr is carried in my pants pocket or on my ankle during long stints in the car. That way the smaller gun can be used first since its easier to get out. If I'm ever in a self-defense shooting (unlikely) that requires more than five or seven rounds (even more unlikely), I'll just drop the little guy and go to my BUG (the 1911).
Better yet, I could just throw it at the fella once its empty.