The root page of a website (i.e. http://example.com/) is special in that it is the default landing page. It might contain a lot of different object types.
It might be considered a Website
, or a Blog
etc...
But should it also be marked up as the primary page for the given object. For example, a person might have a blog/website that has many pages - so should the root page be marked up as a Person and include the additional information?
Same applies for other Things
like Organisation
, Book
, Event
etc etc
Basically the idea is to indicate to things like Google that this root page on the website represents the primary place on the Internet for this person. I.e., this is the persons website...