Ah, so Apple is linking the feature of finding _my_ phone with reporting on lots of others? That explains why people turn it on, but I find that creepy.
The technology is also built so that the location is encrypted for the device owner - so Apple doesn't have a database of the location of every Apple Find My enabled device in the world, which for me makes it not creepy - my devices can find my devices.
It's really useful for locating lost headphones, laptops, etc. -- whether stolen, left on public transport/taxi, or left at a friend's house.
Is there any independent analysis of this end to end encryption of location data, that confirms that Apple can not really access the location even if they want to?