Another use...
It's also like the resistance spring out of a suntour coaster brake, or nankai freecoaster (among others).
In a coaster hub, it helps provide "lag" so that when you crank the pedals forward, it kinda makes the clutch ride up the helical bit of the driver and bite against the inside of the hub shell and get the friction needed to drive you forward, and it's spring loaded so that it sorta floats when the axle is turning. At least I think that's its purpose
According to
www.free-coaster.com, it provides: "Resistance (There must be some kind of resistance, usually a spring, against the axle so that the hub can “tell” the difference between pedaling forward and rolling backward). "
Brian