They demonstrate compliance, impact resistance and the dynamic nature of their control algorithms. It will not break, and it'll keep it's balance. Compliance is

They demonstrate compliance, impact resistance and the dynamic nature of their control algorithms. It will not break, and it'll keep it's balance. Compliance is also a safety feature when the robot is working around humans. Most of the mechanical design, including gearboxes, must be designed to resist outside impacts, because these impacts cause much larger torques on the joints than the motors itself. It's much easier to make an 'animatronic' robot which has pre-programmed motions and can't withstand mechanical impacts.