going all the way back to my AIT-engineer heavy transport days (before i went into armor) , i always liked the tailgate options provided by the M51's and M817s of that era , and the fact one (strong) man can move the tailgate into each of the positions by himself
when out on field projects we operated with the tailgate in the "rock box" position, unless we were doing "metered" tailgate spreads of material along a road surface such as stone, gravel, or asphalt .. to this day i still operate the dumps that way unless i have a need to do a spread .. It's also handier to end-load with a rope drag-shovel (backhoe) or hydraulic excavator when in the "rock" position since the boom doesn't have to be lifted quite as high .. That extra foot of vertical free space can be a tailgate-saver when an excavator operator gets fatigued
i also appreciate the capability of the bed to go (almost) straight up , however this doesn't guarantee certain material won't stick
