I've never had a FB account, but some years ago I got an email from FB listing a number of my friends and family and saying, "All these people have FB accounts. Wouldn't you like to join FB?"
The email included a reply option labeled "don't contact me again," which I chose and then replied. But a few months later I got the same invitation.
Needless to say, I found that to be deeply disturbing, and it confirmed my determination to never subscribe to FB. Later I learned about the phantom accounts. I'm sure FB maintains a dossier on me to this day.
All that clicking that link told Facebook is that you're a real person who reads their emails. It's like when you pick up the phone for a telemarketer, now they know they can continue bothering you because you're a real person and you answer your phone.