At one time, Facebook didn’t allow simultaneous log in on different computers and locations with the same single account. If you are already logged in on a PC and you try to log in on another PC using the same account, the first log in will be exited.
But when Facebook changed the security setting features for the purpose of giving us more control on our security, logging in on different locations using one single account is now possible.
I have tried this using my own personal FB account. I first logged in on my laptop then log in using the same account on my PC. The result, i have my account on two different locations. Though, each log in is somewhat independent from each other. Meaning, you can open any pages on the account without being noticed on the other computer.
But you can actually see the exchange of messages in the chat box on the second location while the messages are made on the first location. This will somehow violate your privacy if ever someone has successfully logged in using your account by any means.
To prevent this, you must put an end to the activity of your account on the other location.