This is a site maintenance category for managing templates which do not have any documentation. It lists templates which include Template:Documentation but do not actually have a written documentation page.
Templates that do not have documentation should have documentation written so that people can learn how to use them correctly. You can help out by writing the documentation if you understand MediaWiki's template system. If a template is badly designed or otherwise incomprehensible then it should be marked with Template:Delete unless it is currently in use. Bad templates that are still being used should be rewritten or replaced if possible.
Templates without any categories at all (Special:UncategorizedTemplates) are likely to be lacking documentation as well.