I've gotten back in touch with various people over the years. I can't predict which of the couple hundred people I will have a reason to reach out to in the future. But I know I'll inevitably be happy to be connected to this or that person on Facebook when I pick up a similar hobby or visit a certain place or go looking for some new type of job, etc.

And no, obviously not ever person I know is worth emailing or calling on the phone on some regular basis. That doesn't mean I don't want to know them.