On the 737 we leave the EDPs on even when shut down as recommended by Boeing to increase system component life.
You leave them on because they are "powered off". If by component life you mean the battery, then yes.
I was referring to inadvertent actuation of the nosewheel steering in case there was a problem with the lockout pin.
Unless somebody grabs the tiller and intentionally moves it there is no risk of injury to the ground crew. The only thing which will happen with NWS pressurized for push is the A/C will go backwards in a straight line, the first sign of "trouble" will be when the ground crew attempts to turn the aircraft.