Should RO'S be left with water in or not?

As the title states, should the RO'S be left containing water or are they OK dry? I have an auto cutoff solenoid valve and when full cuts off the water and the membranes drain of water until needed next? 

Is this good or bad practice? 

My understanding is that it is not good for them to dry out.

I think generally the majority of the water may drain out of them but they will still be wet/ damp for weeks , if not used so don’t see a problem. Just give them a flush through for a few muinits before filling that’s what I have done fir the last 15 + years and never had a problem only changed the membrains even 7-8 years ,so must be doing something right ???