Originally it was sold by GM to be used in limited slip differentials to make them slip. In the early years the technology was not as good as it became and many times the plates would stick and if it became bad enough it was almost impossible to steer around a corner. Both axles would want to turn at the same speed as if you had no differential. One tube of GM Moly Lube (moliybedinum dissulphide) and voila all fixed.
