I would leave them down to (a) take weight off tyres and prevent flat spots
(B) security as someone trying to steal it won’t be able to move it.
you could just spray exposed rams with silicone to protect them
After reading here on the forum I decided to leave ours down, as an additional security aid. However, that's not strictly true, as soon as you release the handbrake the rams retract instantly, and I mean instantly. Still leave them down, as a deterrent as much as anything.