Facebook is a lot more than connecting with long-lost schoolmates, people you met while travelling or relatives you see only once a year. It is a great way to connect with people who have similar interests.
If you were to take a look at my personal Facebook page (the one that only I can view) then you would see a long list of groups that I belong to. There are open groups - ones where you can simply click join, closed groups - where you have to request to join, and a few secret groups - where only those who are members know it exists.
If I were to log my Facebook hours, I would probably find I spend most of my time in these groups, discussing subjects I have a common interest in, rather than trawling my newsfeed to connect.
The beauty of groups is that if you have a group of friends, or even family or work colleagues, you can set up a secret group to enable more cohesive communication. One such secret group I am in is for mums of babies who were due the same month as my son. This kind of group is not uncommon and tends to spring from forums, such as Oh Baby. It allows individuals to share more personal information than they may feel comfortable with in an open forum setting. It also allows for different subjects to have their own thread, rather than being a continuation of just one, long thread in a forum situation.
This particular group I am in has been around for almost two years. It has been an opportunity to share milestones, photo-bomb without losing friends and ask questions or share concerns. From this group, three more have sprung up; the group's friendship has evolved beyond the babies (well, toddlers as they are now) we had together.