The rear axle torque tube assemble is connected fairly rigidly to the engine/transmission assembly. When you accelerate and brake, it tends to push the whole drivetrain forward and aft. The clutch linkage is a mechanical setup so this movement of the drivetrain is separate from the pedal assembly which is fixed to the frame. This can lead to chatter at the clutch plate, so they are often referred to as anti-chatter rods or stay- rods, etc.