Originally Posted by
Bravo73
Yes, on certain helicopters (if they are specifically designed for it). The S76 is one.
The S-76 has a very powerful rotor brake; although everything remains "engaged", it can prevent the rotors from turning at engine idle. It's very useful when embarking/disembarking passengers. In strong & gusty winds, it's reassuring to be able to start the engine/s to idle without the rotors turning. Once they're stable, releasing the rotor brake and advancing the ECLs gets the blades quickly through that uncertain phase where you're not really in control of their flight path.
The original RAF Puma HC1 used to have the facility to disengage one of the engines and run it as an APU. Unfortunately the de-clutch mechanism proved to be unreliable in flight (!) and so the facility was removed.