The "benefit" is that the calc. views marked as dimension can be used as dimensions in calc. views with star joins. Also, dimension views don't come with default aggregation unlike fact-views.
Semantically this is the very same as attribute views and doesn't promise any performance improvement (or degration).
At this point this is more about being able to develop your whole information model as a set of calc. views and still having clear semantics defined for those.
- Lars