Facebook is taking a page from the books of so many social networks before it and prompting users to complete their profiles upon logging in.
Here's what you may see at the top of your homepage when you log in to Facebook (screenshot courtesy The Next Web). May see, because this is just a small test that Facebook is currently running:
As you can see, the prompt not only tells you how close you are to "completing your profile," but it also allows you to answer the questions that Facebook asks right in the prompt, instead of taking you all the way to the information edit page on your Timeline.
Of course, Facebook isn't the only social network that has asked users to make sure their profiles are as complete as possible. Google+ is still doing it on the right-hand side of the homepage:
LinkedIn has been doing it for years. They've just recently given you a cool little "Profile strength" meter inside your actual profile, though:
And ever since Twitter unveiled their new header photos, they've been pushing pretty hard for users to complete their profile by adding one of those.
The point is, this is a common thing among social networks. They want complete profiles. Complete profiles give them more information about their users, which can be used for a variety of tasks. Of course, that includes ad targeting.
But in the end, you want a complete profile, right? Otherwise, what's the point of being on the network? Ok, so you don't want to give Facebook your hometown. Fine. Just click the "x" on the prompt and forget about it.