...turn off the gas petcock when you park your bike? If you don't, why don't you think it's necessary?
I'm comfortable leaving the fuel supply valve on, on any stock harley with a diaphragm style fuel valve, have done it for years and never a problem. That's just me, it doesn't hurts a thing to turn the fuel valve off if you're so inclined.
left on my 93.. pingel came w/ tank i just would forget, pingle never failed. i would turn off in winter.