Categories have long been staple in Dash, even as far back as when it was called JBlogs. In BalfBlog 2.1 they got a major overhaul that meant that posts in categories could be easily located. Now in Dash 1.0 they've been promoted.
When I say promoted I mean they have gone from being just attached to a post to being a separate entity. Categories are now numbers and have names and now have their own table in the database. This doesn't mean a huge amount but it does mean you no longer add categories from the new post page but from the dedicated category management page. Overall this improves performance when listing all categories.