In the additional section of 3.17 Include expected and beneficial files https://w3c.github.io/sustainableweb-wsg/#include-expected-and-beneficial-files there are these two points:
Conversion: Robots can be used to target specific search engines, helping to ensure content is correctly indexed to get a good placement so that visitors can find you easily.
Transparency: The humans file provides credit to people involved in a site's creation, and security offers critical points of contact if an issue is discovered. Both are valuable additions to a project.
I recommend making it more clear what files are being discussed, by naming them, instead of just saying no extension. This is such a tiny suggestion but when I read this today I wondered if we were talking about Robots as crawlers or whether it the the file robots.txt.
Conversion: The robots.txt file can be used to target specific search engines, helping to ensure content is correctly indexed to get a good placement so that visitors can find you easily.
Transparency: The humans.txt file provides credit to people involved in a site's creation, and security offers critical points of contact if an issue is discovered. Both are valuable additions to a project.