Facebook friendships are easier to manage than real life friendships, because you can have ongoing discussions with a Facebook friend about almost any subject. Although your facial expressions can't be seen, you can get your point across better, as long as you think through your comments and be sure to make your point clearly.
Maintaining live friendships takes far more effort than managing Facebook ones. That is because finding the time to make a long call or have lunch with a friend can be hard, but finding a minute to "like" a comment or type a quick "hello" on Facebook is excessively easy.
Real life friendships require that we take time regularly to listen to and respond to the friend in a meaningful way. Though this does not necessarily have to be done face to face, it does require time spent on the phone, by letters written, or by time spent together, in person. In these encounters, we are expected to listen to everything the friend has to say and respond appropriately. This can be time-consuming, and also can involve a lot of emotional involvement which requires energy. With a Facebook friendship, we can choose to skim through the friend's comments, and click "like", while maybe typing a few words, now and then, to them. This should be sufficient to maintain the relationship. We can choose to spend very little time on this, if we wish, and, since the computer creates a distance between us, we can also easily maintain emotional detachment, if we wish.
I have a Facebook account so that I can log in to other accounts easier. I have friendships exclusively outside of Facebook. I never even try to maintain "friendships' on Facebook. Maybe I am old school. But I have always found it more fun to meet for lunch than to type back and forth.