For backup operations, any file and folder that the logged-in user has read-access to. If you can open the folder in Finder and see its contents, and open the documents in an application, they can be backed up by ChronoSync. This typically encompasses everything in your Home folder.

For synchronization operations, you will also need write-access to these files so they can be changed. You typically have read and write access to the same files so this is rarely a problem. You should be careful about synchronizing the contents of your Library folder with another computer, however, since it typically contains computer-specific information.

ChronoSync also has the "Local Volumes (Admin Access)" option that can read & write to any file or folder on your system provided the user has administrator credentials. If connected to a remote computer via ChronoAgent, you can also gain full access to all files and folders on that computer as well.