Beyond Compare works with networked drives, and FTP servers. And, in Pro edition, Beyond Compare can directly access the APIs for OneDrive, Dropbox, and the S3 storage at Amazon.
Beyond Compare can save time by only syncing the folders that match criteria set by you, such as name filters, time of creation, and other criteria. This is a short article describing how to use some of those features.
If Beyond Compare is already running, hit Ctl T to get a new session, choose FolderSync, and then load your source and destination drives.
Most people will have their files on a local or network drive. In that case: select the folders of interest via drag-and-drop or by browsing to their location manually with the tiny manila folder button below the Rules button.
FTP, OneDrive, S3 Amazon, or Dropbox:
A few users will have their files on an FTP server. They should
1) set up the server location: Tools->Profiles->[+] to add a new profile
2) in a FolderSync window, browse to your FTP server using the manilla folder button
If you open something large on your panel it will take a long time to open. For your first sync you should try a test copy of something very small. Right click a folder and set this as the new base folder.