Instead of using hardcoded links, this allows you to set a parent document OR all documents with the specified module / controller /action assigned.
It's url will be used as prefix to the pattern; [document->getFullPath()]/[pattern].
Besides that it works exactly like static routing.
Remember that, when using a controller and action to set the parent document, the reverse url will be that of the last document with that controller and action in the navigation tree.