For users who have not transitioned over to the redesigned News Feed, Facebook is prompting them to add friends with whom they don’t talk much to their acquaintances lists. Users on this list are then designated as low priority and will show up less often in News Feed.
By adding users to acquaintances, it tells Facebook that you’re not that interested in seeing many posts from them. Conversely, adding friends to close friends will make more of their posts show up in News Feed.
Readers: Have you seen this prompt?