As long as the float and needle and seat are working you shouldn't have to worry too much about shutting the fuel valve (petcock) off. That said, you have to consider that even the smallest piece of crud that can find its way to the needle and seat (float valve) will keep it open and you'll flood things. I always shut off the petcock when I park the bike. The hardest thing is remembering to turn it on when you're ready to ride again. It can be very embarrassing, even to yourself to 'run out of gas' if you forget to open the petcock.
This is a reason we always suggest to install an in-line fuel filter. Clean fuel will reduce the probablity of clogging or blocking the carburetor passages.