The advantage is in eliminating the collateral structure in the tug itself, and placing its motive power in the wheel of the a/c. So we save carting around the frame and wheels of the tug. For this benefit we pay mightily for developing and certifying a small and exotic engine to carry around the sky.
There is NO free lunch. Energy is costly, and whether it comes from being stored in petroleum or battery (solar generated, or petrol), the cost cannot be eliminated from the equation.
Find the thread elsewhere in this website for the done to death ramifications of toting a million dollar motor around the skies to eliminate diesel power on the ground.
You make the call.