After introducing the 'close friends' and 'acquaintances' listing options last fall to a rather lukewarm reception, it was clear that the functionality was not something people wanted to waste their time with. Well Facebook thinks it has the answer, with the 'Acquaintance List' suggestion box.
Classifying the closeness of your friends is something you do psychologically, which is why the functionality of manually entering a list of people based upon their relationship to you is counter-intuitive. Instead, Facebook have automated the process of figuring out the definitions of people in relation to you, for you, by collating a list of friends you don't talk to often, and suggesting you add them to your list of acquaintances.
By doing this, fewer posts will appear from them in your news feed compared to those who remain classed as a 'friend.' For those with friend numbers in the 4 digits, suffering from a social overflow (from the 99% of people you've never met in real life), the acquaintance list will form an option in the drop down menu in your news feed, allowing for easy categorisation.
This seems to be a technologically literal translation of something that happens psychologically, alongside the software trying to define people based on pure quantitative information. The idea of lists has just seemed pointless to me since the beginning. The automation can never possibly understand the reason why, for example, you'd keep a person who you find funny on your list of friends rather than acquaintaces. Plus Facebook have already made an unsubscribe button, pretty clearly setting out the idea of a friend you find annoying (or 'acquaintance') without adding a needless implementation.