Have you actually looked at the switch to be sure it is NOT a three way switch for something? Switches by back doors are usually 3 way or they control something outside the house.
Licensed residential and commercial plumber
I put several outlets under the eaves for roof de-icing cables that are wired to switches. Those switches however I put in my wiring closet as I didn't want someone to turn it on by mistake and run up my electric bill.