If you have the Transmitter off with the when the airplane (reciever) is powered. the control surfaces will start moving
on their own and can cause damage to the servos by overdriving them, or cause damage to the plane itself, also if the engine
is running it can throttle up and run away, I dropped a transmitter one time and the battery cover fell off when I was on the
flight line, battery fell out when I picked it up. funny to see a guy chasing after a plane when it was acting up.