Exact Sync
As default, FS executes incremental (simple and non-destructive) synchronizations. This means that: The two folders will contain the same files but most likely this is not what you really want. Probably, you want FS deletes the orphan file "x" too, that is: This is very common in case you have to sync to e.g. a mail folder, a contacts folder, or a folder containing setting-files required by a given application. That given application can run properly only if the content of its folder is arranged properly, so its folder must be exactly synchronized. If you want this, you have to execute an Exact Synchronization. But be aware! Since the Exact Sync can delete files, it's better that you understand well how it works. So, please read carefully the following important notes.

Exact Synchronization
Since the Exact Synchronization can delete files, we would like you pay attention to the following notes. So please let's make a test on two just created folders containing few files just created for this test. Create a file named "y" within the source folder.

At the end of any Exact Synchronization task, FS creates and saves to the computer it is running on, exactly to

(Home)/Library/Application Support/Softobe/FoldersSynchronizer 4/ExactSync Indexes/FS3ExactSyncIndex 1.plist

an index text file listing all the files and folders the two main source and destination folders contain separately. You don't have to open this file. It's for internal use by FS. At the next exact sync, FS uses this index file to understand whether a file has been deleted or added by the user.
FS scans the source and destination folders and finds a file "y" inside the source folder and doesn't find the file "y" within the destination folder. This could have been caused by two different reasons:

If the file "y" is not listed in the FS3ExactSyncIndex file, this means that the file "y" has been just created by the user within the source folder (case A). Thus FS will copy the file "y" from the source folder to the destination folder. If the file "y" is listed in the FS3ExactSyncIndex file, this means that the file "y" existed and that the user therefore deleted the file "y" from the destination folder (case B). Thus FS will delete the file "y" from the source folder too. If you marked the check-box "Preview" in the FS Preferences panel, now you can see the Preview window listing the file "y" as a file that FS is going to delete from the source folder. You can Stop or Continue the sync, as you desire.

• In order to the Exact Sync works well all the time, you must not change the pathname nor the name of the main source and destination folders.
If you do that, FS will execute the next Exact Synchronization as it is the first Exact Synchronization on those two folders, so FS will not delete any file (as written above). So it's not risky. Only, you will see some file you deleted, reappearing because FS has copied it back. Also, please note that the FS3ExactSyncIndex file belongs to the user who did run the Exact Synchronization, so, if you change user after the last Exact Sync (logging in as different user or as user "root" or run FS as root), and you Exact Synchronize again the same two folders, the Exact Synchronization will run as the first Exact Synchronization.

• Please keep in mind that if you delete a file from the source folder, FS will delete that file from the destination folder, and vice-versa. There is no way to undo this task, so please take care with the Exact Sync (and with Exact Backup too).

• Last, take a look at the Conflicts panel and see how to manage special cases like when both the files have been modified after the last Exact Sync, or when a source file has been modified while its parent destination folder has been deleted.