|This is not an official policy and may only be the view of one user. Discussion is encouraged.|
- Flat namespaces are easier to navigate
- The fewer levels of hierarchy the better when dealing with collaboration
- People can't collaborate if they can't find what they are looking for
An encyclopedia is a classic flat namespace. So is a dictionary.
The names of pages in MediaWiki.org are not like the entries in an encyclopedia or dictionary because the topic of MediaWiki is narrow and deep, not shallow and wide. That is, it has few general topics and many more sub-topics. Therefore, keeping a flat, easy-to-navigate page namespace on MediaWiki.org is not as easy as for Wikipedia.org or Wiktionary.org. But it still is important to keep the taxonomic hierarchy on MediaWiki.org as simple as possible and as flat as practical; good management of information complexity helps all users.
Subpages can hurt site usability because they can make it (a) difficult for newcomers to guess where in the hierarchy something can be found and (b) difficult for veteran users to remember and to type the path to a page.
Categories and other labels should be kept as short as possible so paths to a page remain easy to read, to navigate at a glance and to type from memory.