The rotor blade harness ranks as an essential accessory for full-size helicopters. These items prevent the blades swinging or rocking, and thereby exerting pressure on the rotor shaft. If that were to be allowed, in-flight failures could be attributed to it.
Rotor blades set in motion by rising winds could also be damaged by striking obstacles. The rotor blade harness is attached to the tail boom and / or the skid tubes; this is a safety measure, but keeps the helicopter ready for flight at short notice.
It makes a good-looking accessory for any model, and looks great when your helicopter is parked in the pits.