I haven't ordered one, but I could see it being useful to give access to certain people at certain times. Like if you're using AirBnB you can give someone temp access, or if you want to give new employees access to the office without having to make more keys/cards.

edit: You could also use it to detect when the deadbolt is used, presumably when someone you know enters/leaves, since a burglar would probably not use the deadbolt ;)