The Mule Knot (a.k.a releasable knot) is ideal to lock off the rope on the belay plate. There are many occasions in climbing when, belaying from the harness using a device which does not self-arrest ...

While some have brought a long rope and made a 'safety circle' out of it within which a group moves, many others have chosen to ties knots using clothing items of each other to remain connected.