Sorry for any confusion: I have edited my post above to change the reference to momentary switches.
Personally, I use power allowance because I only want to have to make the specification once: I don’t want to have to remember to put the “off” into every Automation and piston that uses that switch. And because I think it’s smoother for scenes. But that’s just an aesthetic choice.
As a practical matter, it also allows the same switch to be toggled by voice. And it allows me to group it with other devices as a follower using the mirror function. Basically once power allowance is set up I know no matter how I turn the switch on, it will always turn itself off again, just as a momentary would have.