Before I was an LEO I carried two guns out of habit.
I have seen situations, or talked with those it has happened to, where the Primary has failed, Primary arm has been wounded, Primary Gun has been taken away as well as needing to arm a third party.
My Agency allows me to carry whatever I want off-duty, as long as it's not full-auto. I carry an N-Frame Revolver as a Primary with a reload and a J-Frame and a reload as a BUG.
If you learn how to "dress around the gun" it's not that difficult. By the way, it's over 100 degrees here today and I have two guns on and I'm outside a good bit.
Biker