Describes in detail the Remove Deleted Files setting.
If this box is checked, any files that are deleted on your computer will also be deleted from the backup copy (in your Home Folder) the next time a backup is performed. If the box is unchecked, files that are deleted from your computer still exist in your backup copy until you manually select and delete them from your Home Folder.
If you frequently create and delete large numbers of files, enabling this option (checking the box) will help to reduce the amount of space your backup data is using. However, an error reading the files on your computer could possibly result in deleting all of your backup files! The recommended default is to leave this option disabled (unchecked).