You said that you couldn't find evidence of the use of alternate weapons in a real situation.
Here's the story of the infamous 1986 FBI Miami shootout with at least three instances of lost guns, the use of backup, multiple and the other guy's weapons.
All in a single and well documented incident.
Judge for yourself the merits of being capable with more than just the one you carry.
(And hope the bad guy isn't).
http://www.thegunzone.com/11april86.html