Cork,
Reasoning for keeping levelers/jacks etc. up or down, varies between circumstances. It certainly won't hurt them to be down for short or, long periods. It all depends on what your intensions are when it's sitting. If it's at home and going to be parked for a bit, and, you'll be doing some cleaning/repairing/maintenance or more, it will be more stable if the jacks are down.
If you're not going to be inside at all, and, you may only have it in a specific spot for a short time, there's really no need to put them down, unless you just feel better about having them down. Now, as has been stated, if you're going to have the fridge remain on, even while it's parked at home, then it of course, must be level to do that and, that requires the jacks to be down.
Scott
Scott and Karla SDFD RETIRED2004 Itasca Horizon, 36GD Slate Blue 330 CAT
2011 GMC Sierra 1500 Ext Cab 4x4 Toad
2008 Caliente Red LVL II GL 1800 Goldwing KI60ND