Many wikis don't have a good "portal" page — a single page that quickly lets you understand how much content the wiki has, and if there's a lot of content there, helps you focus on the content you're interested in.
The pages in this directory help do that.
For Mediawiki-based wikis, good places to look are:
how many pages / users / edits does this wiki have?
- popular pages
- Special:MostRevisions most edits
- popular categories
- Special:MostLinkedCategories most child pages