If you don't dump the air, it will typically start to leak down after awhile. Some leak down in a few days, some may take weeks. This all depends on how tight all of your air fittings are. There are many fittings from the dash to the engine and you'll always have some that leak a little.
Whenever we come home from a trip, (park alongside our house) I cover the tires, mirrors and wiper blades, turn off the Oasis and plug in the coach. Once this is all done, I dump the air (no jacks).
So.....to answer your question, dump the air when you're storing the coach.
Don & Mary
2019 Newmar Dutch Star 4018
2019 Ford Raptor