[Alex.Norton]

I wouldn't really make it much more efficient because the energy is still in the system it is just keeping the gear turning instead of the robot translating.

The energy will go towards making the robot move when you turn the motors off and let the robot come to a stop because this is when the robot will come to a stop.

In a car since the engine isn't connected to the ground and the fly wheel keeps turning when the car comes to stop this just adds inefficiency to the system but for a robot and an electric motor it doesn't have nearly as much effect on efficiency.

By the way, thanks for the question. I've been enjoying thinking about it.
Alex