HTTP Vary doesn’t need to be used for varying mobile only pages
If your mobile pages vary by user agent, they don’t need the http vary user agent in the headers.
Use X-Frame-Options: Deny to Prevent Pages Appearing in IFrames
You can prevent your pages from appearing inside iFrames for security reasons, by including an ‘X-Frame-Options: Deny’ in the http response header.
Good Quality Category and Tag Page Can Be Indexable
John supports good quality ‘category’ type tag pages which are valuable to users and worth having indexable.