I breathe from it prior to every dive, I breathe from it when practicing air sharing drills. Outside of that, I use it as my backup reg, If I am on back gas, I am breathing from my primary, that is what it is for.And a necklace reg is for looking like a cool Tek Diver?
I use my backup during safety stops to make sure it works beyond a few quick breaths during an s-drill at the beginning of a dive, to make sure that the necklace isn't too tight for wearing for more than 10 seconds, to make sure that the zip tie on the mouth piece isn't stabbing me in the lip the whole time, to make sure that cockroaches haven't eaten away at the diaphragm causing it to breath wet.
You know... verify it will actually function as well as your primary when you need it. How else do you do all of that if you never breathe off of it?
How you use your regs is up to you, but to say it needs to be on a break away to circumvent an emergency caused by incorrect usage of gear seems pretty silly to me.