I have unfollowed a few people from time to time when I just don't want to see whatever it is they are posting obsessively (one was posting lots of graphic photos of abused animals, another was posting graphic photos of alleged aborted fetuses, etc).
I have only ever once actually blocked someone. A former classmate I knew in third grade and then again in highschool. He was building an off the grid shelter, collecting guns and posting all kinds of craziness about civil wars and him planning on fighting, etc----I felt he was truly unstable and did not feel it was safe for him to know where I or my kids are, etc.