As a developer pointed out once, namespaces are meant to disambiguate two different pages that otherwise would have the same name (just like namespaces in some programming languages) 
If you think of them that way there are valid use cases like the ones I mentioned in this thread:
Instead to organize things hierarchically there are better alternatives and indented blocks is one of them. When it comes to pages, the concept of indexes that I described later in that thread is the best one to organize pages hierarchically, in my opinion