The H-53 was designed as a naval helicopter for shipboard ops. Both (or all three) engines could be started with the rotor brake on, then released to minimize the time at slow rotor rpm in gusty winds. On shutdown there was a minimum speed for brake application to avoid suddenly stopping the rotor head. It could even be applied with an engine still running.
Unlike the disk break setup commonn on other types, the huey brake had a spline directly into the gearbox. Bell's idea was to only use the brake at at low rpm. During a rapid shutdown on a UH-1 I found out that the rotor brake was indeed more rugged than the transmission gear it slowed. I got to see the chewed up gear myself when they replaced the gearbox.