I'd never leave my computerized machine in my car for several reasons. First, I'm Canadian, so dealing with cold winters and computers don't like cold. Even my old manual (vintage) machines don't like the cold, they have to warm up to room temperature or the belt inside just won't run.
Also, cars get broken into. I've had a theft from my vehicle (actually they took the whole car!) and would be devastated if my expensive machine went on a joyride.
Also, computerized machines don't like to fall over. Unless you had it tied down in the trunk, I could fall over when you go around corners or if you have to slam on the brakes. I may go overboard, but if I have to put my machine on the seat in the car, it wears a seatbelt!