Let's assume the user wants to see all notes from their follows. The problem right now is (as some people have already commented in Will's note) the user sometimes scrolls for a few minutes, then puts the phone away and starts scrolling again in let's say 15 minutes. What happens when you come back is there are some new notes, but after scrolling through those, you need to scroll through the "already seen" posts from the previous session very quickly to be able to see notes you had missed previously. If you repeat this many times a day then the problem scales to a point where the user gives up and accepts missing a lot of notes that day. Having a boolean read state for notes fixes this problem. There could be a toggle or an eye icon for toggling already seen posts as hidden/visible. Some RSS readers have this functionality.