" if one leaves the RB fully applied until the rotor stops, it stops very abruptly, possibly putting inappropriate loads on the drive system."
There was a 212 that had a tooth come off somewhere in the main gearbox because of this practice. My own practice is to ease the brake off at about 10%, if i use it at all.
The lower limit may be there for the same reason that the yellow band on the NR gauge is there - to stop inappropriate vibrations on the old one-piece tail rotor drive shaft. Just another thought
Phil