It is used to build and maintain a list or lists of pages—primarily for the sake of the lists themselves and their use in article and category maintenance. It is not part of the encyclopedia's categorization scheme.
These categories are used to track, build and organize lists of pages needing "attention en masse" (for example, pages using deprecated syntax), or that may need to be edited at someone's earliest convenience.
These categories also serve to aggregate members of several lists or subcategories into a larger, more efficient list (discriminated by classifications).
Typically, tracking categories are automatically populated by templates invoked in pages or by the MediaWiki software (see Special:TrackingCategories for an overview of the latter).
Administrators: Please do not delete this category as empty! This category may be empty occasionally or even most of the time.
{{Large category TOC}} uses {{PAGESINCATEGORY}} to count the number of pages in a category.
However, as of 1 April 2020, there seems to be some issue with {{PAGESINCATEGORY}} falsely returning zero in some cases. This category tracks all pages where the count is reported as zero (or less), so that the veracity of the number can be checked.
This category should contain only pages labelled as "empty". But until bugs in the Wikimedia software are fixed, it will include some non-empty categories. For more info, see phab:T18036 and phab:T221795.