"When you make a post that is particularly interesting to certain friends, you want to make sure they see it. Instead of tagging friends in the post or the comments section, we’re testing a more discreet option to alert them of your post by sending them a notification."
Ideally, this will clean up Facebook posts so they don't have all those people tagging their friends in the comments section. Also, it should give users more control over what's posted on their Facebook page. And sure, if you have "Timeline Review" turned on, you're able to review tag posts before they show up on your timeline anyway. But, this eliminates the need to review anything, which means there's one less step to deal with.