My 10 year old Bernina has showed no signs of my inattention. It is plugged into a serge protector but I just turn off the machine switch when I am finished for the day or project. The only time I unplug is when we are away. Sometimes it has been left on for a couple of hours? I don't really know because if I leave it on (when another task comes up) I usually get back to it later or go by the room and seeing the light is on, I will shut it off. I don't worry about it being on for the machine, it's more of a waste of energy concern.
My main concern is....opps I think I left the iron on? I never have but I forget. Mine doesn't have the automatic shut-off but after reading about a fire with that kind, I will be more careful!