mixed up,
It doesn't matter whether the fuel is on or off. There's enough fuel in the carburettor for the engine to start, if the mags are live.
If the aircraft moves forward due the throttle being inadvertently left open (this happened to a colleague recently) it could mean the difference between recovering the aircraft from a few yards away or recovering the UAV from a miles away.
Also, turn off the fuel when sucking in, in case a mag lead has failed to live.
Which is why I say, never move the propeller with the fuel on.