Also supposed to be good for towing heavy stuff up long hills - stops the box continually changing and overheating. That's what the book said.
I'm so incredibly lazy I use the gears to slow down. Saves lifting me left foot.
Also, if you have an older model, brakes can fade on steep hill with trailer. Scream, panic (sorry, quick flashback). Taking it down the hill in gear saves that. Btw the box won't change down if you're going too fast.
OFF road, most people would rather take a steep down slope in bottom first rather than rely on Mr LR's AHD, wondrous though it is.