In other words, the use of xml/categories forces every Weblog Author or Editor (perhaps the word is Author) to consider the audience from a structural perspective each time a piece is developed, particularly in the early weeks of the development of the blog's basic style.
Categories are extremely useful for knowledge-management applications. They give an 'Author' the ability to tell a specific group of readers that all of X sort of material will appear in x section thus allowing the development of discrete conversations about subsets of the overall architecture.
XML creates the opportunity to keep that question open for a while as the blogger develops a real time feel for audience structure and composition. via [5th Constituency]