It is EXTREMELY important! It means you have a project setup with Worksets, and that a Central Files resides on a server.
You are working in a local copy, with your Revit user name, and are editing parts of the model which are separated into Worksets. You make edits and changes, and then Synchronize to Central, which publishes your edits back to the Central File.
If you are working in a team, the other users do the same--which enables multiple users to work on the same .rvt file
simultaneously.
Do some research on Creating a Central File, Worksets, Relinquishing, Creating Local Copies and Synch to Central.
This is a CRITICAL part of Revit that you MUST understand.
cheers
