This option ejects or unmounts any of the disks used for the synchronization when copying is complete.

Only removable disks can be ejected; non-removable disks can be unmounted. When a disk is unmounted, its icon disappears from the desktop until the disk is remounted or the next time you restart your Mac.

This option is most commonly used to eject a floppy disk when synchronization is complete.

The disk containing the active System Folder cannot be ejected or unmounted.