As with any other type of 'gear', it remains up to the individual to do their own risk/needs assessment and determine both the desirability and practicality of carrying 'backup' gear items.
I don't carry around a spare pair of footwear or cellphone.
Joking aside, I do usually carry a spare folding knife, but that's more for the practicality of having cutting options (plain edge vs serrated edge, size of the blades for the tasks, etc).
The technology and reliability of most of today's firearms, notwithstanding whether someone has tinkered with one and rendered it different from how it came out-of-the-box, is quite a few technological steps ahead than the guns (and ammunition) of yesteryear.
Sure, having a secondary handgun available might prove prudent or advantageous under some exigent circumstances, and it's been recognized in LE that it might prove beneficial. Many agencies have either authorized them, or even issued them over the years.
All of that said, it's still wise to remember the importance of adhering to policy (LE), or local law (or licensing restriction?), regarding carrying more than 1 concealed handgun.
I don't often do so anymore, now that I'm retired. My daily risk is a bit different than when I was carrying an active badge and continually being sent to reported, or known, violent situations, etc.
Since lawfully carrying 1 handgun comes with the normal inherent risks - (security of carry method, retaining control of it, maintenance of both gun and carry method, etc) - it does double the usual things to consider when upping the number of handguns being carried.
Basically ... TANSTAAFL.