Not an offroader, but I believe it's to avoid sinking deeply into sandy terrain, similar to wearing snow shoes in deep snow (Also a reason to air down your tires).
I think it also makes it easier to rock crawl over larger rocks.
You aren't alone. I preordered in January 2020. I picked the LE R1T, El Cap Granite/Ocean Coast Interior. However, I might end up changing colors/interior. I really want to see them before comitting.
I've been planning on the 135Kwh battery, as I believe it's enough for me. I have also been assuming the 180kwh would be outside my budget, which it may still be. Hopefully Monday will tell.