I usually store mine in the down position too. I put it down to flush it when I get home and then leave it there til just before I tow it off the drive again.
But it helps the water drain while flushing (and subsequently) and then also keeps the oil/fuel etc in the "right" places for extended periods (before tilting the engine and bouncing it around on the trailer moves them again)!
It also means that I can get behind the boat as I back it up to the fence when stored, so leaving it up would put the prop right against the fence.
There's weather out there - must be time to RIB!
(Or dive, or ref rugby, or.......)