Much like Gmail allows to remotely sign out of Gmail from other sessions Facebook added new security feature, Remote log out of Facebook account that allows users to find and log out of other sessions if they are logged onto Facebook from other Computers.
If you forgot to logout from Facebook from public Computer or from your friends device there will be a chance of your account get compromised and bad guys take advantage post abusive stuff and other stuff on behalf of you that may lead to ban of your account of which you are not responsible.
So from now on if you login to your Facebook account Facebook will show your recent account activity in “Account Settings” under “Account Security”.
Recent activity includes login time, device name if you are previously named it through Facebook’s login notifications feature, approximate location of login based on IP address, name of Browser and Operating System used.
Facebook shows recent activity details for other active sessions as well then you can close those sessions by clicking “end activity”.
You can always change your password after ending session of unauthorized access to your account.Facebook says this feature is rolling out to all users gradually, I have got this feature check yours by logging into facebook and checking account security in Account settings.