I just came across one instance where this meta tag was actually used for a purpose:
<meta name="categories" content="work">
A community of web sites at a women's community migrated to a new system, changing the URLs. The old ones had an extra subdirectory for category - for example pages.domain.com/wh/sitename for work from home, pages.domain.com/cp/sitename for computing -and so on.
For the new sites that two letter "community" category was eliminated, changing the URLs to pages.domain.com/sitename but there was a directory of member web sites generated, with categories based on the former "community" -represented by the two letters.
When they migrated, this tag was inserted, apparently for directory categorization purposes, because that is how they are now indexed.