The ror.xml file standard was originally released in 2006 when search engine crawlers where still improving and the file has a real purpose back then, however since then crawlers have become more sophisticated in their ability to crawl content. These days there is no demonstrable benefit to having one.
The ror.xml file contains details on all the content, not just links but also short page summaries, pictures, as well as sitemap info, however as with using meta tags and sitemap files there is no way to directly influence what Google will display. Sitemap's are good in that they help crawlers identify new and modified content faster than if they where limited to organic linking, but having both a sitemap.xml file and a ror.xml file these days really is overkill as functionally, even though the ror.xml file contains more data, all search engines will really focus on is the sitemap aspect (list of site links), everything else is pulled from actual page content and not from resource files.