but I guess that rotor brakes are a fairly recent addition and I don't get to see as many helicopters as I used to (on the ground that is)!
I was a wessex crewman for many years from the mid 70's. The aircraft I was trained in was the Wessex 1 which had been in service for a lot of years (50's I think) before I started and the rotor brake was used as a matter of course. When shutting down the rotor brake was initialy applied gently to slow the rotors and then applied fully once they had slowed to an acceptable rpm obviously taking care not to overstress or shock load the transmission. Once applied it sometimes needed to be pumped to attain the required pressure.