Currently, beyond the built-in division between subcategories, files, or other pages, there is no distinction made between category members which are in different namespaces. Normally, this behavior is ideal, which is why it was made the default years ago. However, there are situations where more specific or user-controlled namespace filtering would be useful, e.g. listing (or excluding) all user pages in tracking categories.
This can currently be approximated with Special:Search using incategory: and limiting results by namespace, though that method requires Extension:CirrusSearch to work, so many third-party wikis probably can't use it. For tracking categories, it can also be achieved by modifying the relevant system message (e.g. the English Wikipedia split up their "Category:Pages with broken file links" into separate categories for ns:0 articles, templates, and other pages, by modifying their MediaWiki:Broken-file-category message in 2011, though @brion noted at the time that it may not work as expected [though I don't know if MediaWiki has been modified since then to make that use case behave better]), though a wiki may prefer to have only a single tracking category for a given tracked error, for any of a number of reasons.