The sole reason I'm making this question is due to the fact that such joints/articulations would allow the electric motors to continuously move while the walking motion is performed, instead of the back and forward movement of our biological counterparts in which such robots were inspired.
I'm assuming that if you keep changing speed in a specific way, you could replicate the same back and forward movement of biomimetic legs without the need to force the electric engines. After all, spinning wheels are supposedly more efficient than legs.
(of course, the examples bellow are for human use in mind, unlike the robots that can be reduced to simple bearings)
The joints/articulations that I'm referring to are the leg ones on these examples: