I know a girl in my year who didn't have Facebook, by the end of the year, it was too much effort and she created one.
Thing is even before uni, people already have group chats on Facebook, for the course and the accomodations. So you get a chance to get to know some people before you even get there.
Majority of societies and such also organise the events on Facebook as that's what's most people have. So you might be the last to know about some events or even miss them.
You don't have to create Facebook and constantly make posts and stuff. Personally, my Facebook is pretty blank and only has my name and my education on it. I don't really post stuff either. It's just something I use for the messenger and to keep track of the different events and societies.