Sadly not linking your address book is probably not enough. I use 1 email address for almost all online shops and site registrations, and sadly I also used it for Facebook. The result? Shops upload their customer data to Facebook (I think it's an FB "feature" so they (the shops) can target ads at their customers), and guess which identifier they use? Yeah, I'm quite sure the customers' email address.

Hah, even if I used different emails, my name is very very unique. And writing this I wonder how GDPR compliant the whole thing is, or if they just trade md5s of emails with each other..