Be careful, this is a trick question.

Many of us "reboot" or run with the ICE off to get the best mileage. You can't use less gas than none. This act may not be entirely safe so please be careful. You lose PS and eventually PB if you leave the ICE off. I've been cutting the key back on to the right so that the fans, turnsignals and dash all work. The HCH has electric PS so you even get PS back. Vettes have regular PS so when the ICE dies so does the PS. With the key in the right most position all the gauges work on an HCH so you can see how great your mileage is. If you turn the key one click farther left you lose PS, the dash, turnsignals and the fans.

So if you are coasting ICE off with the key one click back from all the way right is your car going anywhere?

Clearly the car is moving but I don't think you could prove it from the trip meters or the OD. The car does not know it is moving, correct? So according to the car when you coast a mile you have not gone anywere.

The idea of rebooting is to reboot the car so the gauges and safety equipment still work.

Efficient drivers do it better.
1003 miles a tank personal record. 74MPG calculated. HCH1 CVT

Ahh yes. Rebooting is the safer way to go to be sure.

By not rebooting and coasing with everything dead your mileage at the pump might be a little higher cause you have less load. The displayed mileage should be closer to the real world, and your OD will have a few percent less miles on the total. For any normal sane person giving up the comfort and safety just to squeeze a couple tenths out of a car would be crazy. I've never claimed to be sane and I'm only 2 tenths out of the number one spot in the database for HCHs so I may start givin it a try.

Edit:

I'm so dumb. Whatever slight increase you might get from having the power off the car is not going to record. You would not get credit for any miles driven this way.