What are the useless meta tags for SEO?
The meta tags represent one of the most famous optimization factors. However, over the years, their importance has been decreasing a lot.
The meta keywords tag would not be used by Google anymore, for example Don't waste your time with it and more importantly, don't stuff it with consistent keywords with your page. Your competitors will love help themselves to create (yes THEY will) qualitative content.
The meta description tag would no longer play a direct role in the ranking of a page. However, be careful! You still have to take care of them for the human internet user, they are still a powerful way to « call to action »
The meta robots tags default setting is "index, follow". As a consequence, it is not useful to write it if you want the page to be indexed and their links to be followed.
However, it works quite well to forbid the indexing and not spread popularity (noindex, nofollow) or even to forbid caching of content.
Google seems to ignore totally all the Meta Dublin Core tags.
The same goes for the meta revisit after tags. It is impossible to control the rhythm of GoogleBot visits with it.
Author, Copyright and Subject tags have apparently no impact either on the ranking of a web page.