Yeah, think about it.... You leave the key "on" the whole time you're driving. I don't see what it could possibly hurt, except maybe the battery. But if she fired right up, I don't think the battery is a problem!
I must be thinking of the old days of points /condensor in the distributor.
Back then if you left the key in the on position with engine you could fry up the points.
Geesh, I'm getting old