Your best friend for file transfer.Fetch
The Delete stray items at destination checkbox in the Mirror window instructs Fetch to delete items in the destination folder that do not exist in the source folder when mirroring two folders. This lets you synchronize the two folders so they are completely identical; normally mirroring just adds items to the destination folder or updates existing items, it does not remove items altogether.
This can be a dangerous option, because it can delete entire folders and their contents. If you accidentally select the wrong destination folder and you select Delete stray items, you could lose a lot of files. Be very sure you really want to delete non-matching items from the destination when you select this option, and use it with care!
A warning is displayed when you select this option to remind you of the possible dangers.