Product manager Andrew Huang says the status tags are "all about engagement." He says Facebook wants to let users reference their real-world connections in their status posts.
For example, if a status update mentions having lunch with a friend, the user can tag the post with that friend's name. That'll make it easier for someone to pull up all status posts mentioning that particular friend, regardless of who made the posts.
It's similar to how someone can now easily pull up photos of a friend, regardless of which user had taken and shared the image.