A local RV dealer recommended we use "Store" when the RV is plugged into shore power. But my book says that it goes to a maintenance mode and won't overcharge, so it seems it should be on virtually all the time as well.
Ours is plugged to short power virtually all time time anyway.
FWIW, we left this morning with the battery fully charged, and the battery was at 13 volts. We drove with the switch in "Use" for about four hours, and when we stopped it was at 12.45. I don't know if that's significant or not.
After reading through this, I think we should leave the switch in "Use" unless we really are storing it off power. We do plug in when it's parked at our home.