I do use them on my bailouts (along with an OPV). Bailout regs don't get used much and can get cruddy quickly if water gets in the first stage because it tends to sit there for a while.
I like to keep the system pressurized to make sure water doesn't migrate down the hose to the first stage (particularly since my second stages are seat saver types). Yes, I could dispense with the shutoff and just pressurize then turn off the tank valve, but it's easy to inadvertently purge the air out.
Yes, making sure the shutoff is "on" adds a step, but it also saves me the step of turning on the cylinder. It's just muscle memory. My buddies know they are there (and largely use them on their own bailouts too).
I don't feel terribly strongly about them, but I do appreciate that my first stages do seem to stay cleaner this way.