The Synchronize feature ensures that you are always working with the most up-to-date information. When a new version of a content is checked in, any contents which refer to previous versions of the newly checked in content are flagged, notifying you that their content may be out of date.

For example, suppose a Solver Deck Plane.fem references three include files: RightWing.fem, Fuselage.fem, and LeftWing.fem. Plane.fem version 1 refers to version 1 of the three include files.  

Suppose Fuselage.fem is checked out, modified, and checked in. This results in version 2 of Fuselage.fem being created. Now, suppose you have version 1 of Plane.fem in your workspace. Once version 2 of Fuselage.fem is checked in, you will see something similar to the image below.

Notice that the content image for Plane.fem is flagged, alerting you. Viewing the references, you can see that his version of Plane.fem, version 1, is referencing version 1 of Fuselage.fem, while a newer version, version 2, exists in the library.

Now, you can click Plane.fem and select Synchronize from the content menu. This results in a new version of Plane.fem, version 2, being created, which now refers to version to of Fuselage.fem, as shown below. You are now working with the most up-to-date information.