Good points, but I was thinking in terms of it not burning cleanly and being the source of gunk that could cause the problems you mention.
I've learned to check the very basics first. I've got part way through helping a friend remove the door skin from the back door before asking why he was doing this. The inside door handle wasn't working. Oh, does it have a child safety lock? A what? One of [click]
these.
Then there was the friend who's car had broken down. After ten or fifteen minutes of experimenting, then calling the mechanic service, I noticed the fuel guage on E.
Done this twice, about ten years apart.
Same friend. 