This manual is no longer being maintained for TYPO3 versions 11.5 and above. The majority of the content has been migrated to the Extbase or Fluid sections in "TYPO3 Explained".
Command controllers make functionality available on the command line and in the scheduler backend module.
They can provide functionality for recurring tasks like mail queues, cleanups, imports and more, which is then available for administrators and regular backend users.
Please see Symfony Console Commands (cli) in "TYPO3 Explained" for more information on command controllers.