The height control is pretty sophisticated. As has been said, the -low- mode is only for loading/unloading. My experiences have it raising to -normal- at anything faster than a crawl. It also seems that the shock dampening goes really soft when you go into -low-. I wouldn't recommend trying to fool the system to drive in -low- for any reason. I think it would be unsafe, floaty, and you'd risk hitting your bump stops.
Based on the manual, there's also an extra-high mode that it goes into when you're stuck offroad. I guess it assumes that you're high-centered and need a little extra clearance to get moving.