The distance towed is completely irrelevant. What should be measured is how much energy is put into the battery by towing over a certain distance. An experiment was done where a Tesla was towed by a gas pickup. While being towed, the tesla driver kept feet off all pedals and that resulted in the car applying heavy regen braking. The pickup was making somewhere in the neighborhood of 3 MPG while towing. If I remember, the tesla was then able to drive about three times as far as it had been towed if it kept its speed down. No physics laws were broken because the amount of energy put into the endeavor was much more than the energy the car ultimately used to power itself while using the stored energy. Inefficient? Yes. But so is extracting stored sunlight, in the form of oil or coal and burning it to "make" power. That isn't really the point though. It's all about convenience.