If I turn off the water supply to the hot water heater, do I need to turn off the water heater?

If you turn off the water going to the water heater but you leave the gas on you create a bomb. It may never go off but still it is a bomb. If the thermostat should stick open the fire would not cut off and the heater would fill with steam and it would finally rupture, yes I know that you probably have a temperature and pressure relief valve on the heater but they can go bad also. Like I said it may never go off but there is the chance, so if you turn the water off to the heater turn the gas off also.