One-time passwords make it safer to use public computers in places like hotels, cafés, or airports. Those with concerns about the security of the computer they're using while accessing Facebook can text "otp" to 32665 on their mobile phone and have a one-time password (it expires in 20 minutes) texted back to them to use instead of their regular password. The feature can only be accessed if you have a mobile phone number added to your account.
The ability to logout of Facebook remotely can be useful if you login from a friend's phone or computer and then forget to logout. You can check if you're still logged in on other devices and remotely logout from your Account Settings, under the Account Security section. All of your active sessions are presented there along with information about each session. If someone accesses your account without your permission, you can also shut down the unauthorized login. After that you'll want to reset your password.