Runs the Obsolete Core Files feature: it removes the Joomla! files and folders which a Joomla update was supposed to delete, but did not. Leftover core files can break your site outright, most commonly with a fatal error about a class alias.

This task type has no configuration options.

A clean-up which does not finish inside the task's time limit reports that it will resume, and carries on the next time the task runs. If some files or folders exist but cannot be deleted, the task finishes in a failed state and names each of them in its log, so you know exactly what to go and remove by hand.

Running this task once a week is plenty. Its natural companion is the Reset Joomla! Update task: schedule this one to run after any Joomla update and you will catch a botched clean-up long before it takes your site down.