It checks if you moved folders around, or assets. Thus it is good to regularly fix up redirectors. This is also required when you want to delete something.
Example Usage on Move Folder
When you move a folder often the URLs in the project are not updated. Thus, after moving a folder, right click the old folder and use FUR option. After this you can delete old remaining folder. Sometimes 1kb huge files (not visible in project are created in the folders). These can be erased when FUR has commenced.