Consider this option: ALWAYS on!
1. If you leave your vehicle for 2-3 weeks it can consume your battery, and you have to jump start to start the engine.
2. If some commotions happen, you forget to unplug the camera, it will overwrite all the valuable footage videos....
These stuffs happened to my friend's vehicle, RX350 3018.
Good luck!!!!

 

However, it does have an option in the "Magic Plug," or whatever they call it, to reach down and switch it off without having to touch the camera. This is for people like me who usually keeps the 300h in the garage. So... don't need to record the inside of my garage however, it starts recording the minute you drive off.

 

Not 100% true, there are in line voltage regulators like the black magic pro that monitors your car battery voltage to ensure the situation you described doesn't happen.

I have been using the black magic pro with no issues and where I am from temperature drops below -30 deg C.