If you had the FB integration set up in a certain way, all your FB friends would become entries in your iOS/macOS Address Book. It can make a huge mess.

The problem this causes me is it adds email addresses you can't remove to contacts. And for some reason using Siri on the Apple Watch often wants to iMessage/SMS one of these Facebook addresses instead of the most recently used address for that contact (actually I think the real problem might be more than 1 contact with the same name?)

To make this worse on my carrier (Telstra) these messages go through but Telstra very kindly turns them into an email that I may or may not see until much later

Drives my wife and I a little bonkers. Should probably have filed a radar however I guess maybe it will be moot in iOS11

That's especially fun for me when my phone syncs with my car's handsfree setup. I wind up with all my FB entries (which have no phone #'s attached) mixed in with all the deliberate entries which do have phone #'s. I wind up having to scroll thru 150 or so extra entries on the radio screen just to make a phone call in traffic.

"Siri call <name>"