IMO the best reason to touch the front brake lever and cut the motor is to pass a larger gear with legs power only. Powerful mid motors are strong enough to destroy the mechanics and shifter line switches are not reliable .
I suggest you to read or look at vids. about the chain line of e-bikes (Luna). I personally reduced my 9 speeds cassette to 6. I also touch my brake before shifting to stop the motor.
French dictionaries are full of borrowings from English, probably because it's practical or it comes from the usage, when it's a french word it's by snobbism ! Perception ? ;)
Oh no, they are called "fixies" for fixed gear bikes and they race with them in the middle of the towns. The film Premium rush (2012) is a story about bicycle messengers who work and race fixies.
What surprise me is that a worn-out low energy consomption lap top battery could be good enough for a higher energy consomption scooter. But when you have nothing else do you have the voice.