JW hit the nail on the head, as I am discovering is usual, but here are my thoughts and experiences as well.
FWIW, I’m not a LEO, and carry in a purely civilian self-defense format. When my father-in-law asked me, in a tone of curiosity, why I carried two guns I simply replied “in case one doesn’t work.” I find that answer satisfies most folks who aren’t anti-gun to begin with.
I was always of the opinion that J-frames were pretty much only good for screwing into someone’s ear in a ground fight, but that this was something that could very well happen. Then I ran into a good deal on a used, pre-lock 642-1 and took it to a 10-8 BUG class. Ben Lennett really showed me the capability of the little J-frame, especially combined with CT lasergrips. Am I as good with it as I am with my Beretta or 1911? Heck no, but it will suffice in a pinch if the primary gun goes TU. Which brings me to my next point…
In the BUG class, we did a couple of drills that showed the time difference between clearing a malfunction and drawing the BUG. For me, the difference between clearing a nasty malfunction and engaging the target with the primary, versus simply dumping the primary and going for the BUG, was on average about 4 seconds. When you really need something to go bang, that’s a lifetime.
Another point is off-hand accessibility. I generally carry my J-frame where I can draw it left-handed. This lets me access a weapon if my primary hand is occupied (dragging my wife or son out of harm’s way, or fighting off a grab on my primary) or incapacitated. It also lets me quietly and discreetly pre-stage a gun if things start to look squirrelly. All I have to do is put my hands casually in my pockets, no big deal, no threatening gestures. If I need to, I can shoot through my pocket, or draw and engage with five rounds while drawing my primary with my strong hand.
While some have mentioned the ability to arm a secondary person, as far as I’m concerned, if they didn’t bring their own gun, they’re probably not competent to use mine. Exceptions exist, of course, but it’s not something that I consider within the realm of reasonable possibility.
I don’t find the addition of a BUG to be all that onerous for EDC. I already have two cell phones, a Leatherman, a folder, a primary, a spare magazine or two, a wallet, and my keys. The BUG just means that my wallet gets moved to a cargo pocket.
As the old adage goes, “I’d rather have it and not need it, than need it and not have it.” When you need it, brother, you NEED it.