The new feature, called Login Approvals, requires users to ‘authenticate’ any new device before they are able to log into Facebook from it. That code will have to be entered along with your password to log in. This would only occur the first time you try to log in from the new device.
The idea behind it is that it will prevent hackers who somehow steal your Facebook password from being able to log in to your account, since they would not have access to the verification code.
“One challenge in building login approvals was balancing security and usability. Similar features on other websites require you to download authentication apps or purchase physical tokens to act as your second factor. These are good approaches, and we’re considering incorporating them in the future, but they require a lot from the user before being able to turn on the feature” wrote Facebook’s Andrew Song in a blog post.
Login Approvals is not a mandatory new feature, so if you’d rather not bother with the new verification code process, you don’t have to. For those who are interested, the feature is available from the Account Security section of their Facebook account.