I used to always shut mine off after every use. I guess it’s out of habit from my earlier Triumphs. Anyway over the last 3 years, I have had to replace the stock petcock 3 times now. It gets really stiff and hard to turn when they start going bad. After the 3rd time, I have just left it on. Hasn’t hurt anything yet (been about 8 months since I started leaving it on). I would say either leave it on or buy an aftermarket one which will hold up better if you want to shut it off after every use.

"It's a hundred and six miles to Chicago, we've got a full tank of gas, half a pack of cigarettes, it's dark, and we're wearing sunglasses."