This admin tool clears all backup files from the server. It is useful for freeing up space from dev and test servers once they are refreshed from production.
It also gives a report of how many .mbz files were deleted and how much space was cleared.
The backup files can be deleted from /admin/tool/clearbackupfiles/index.php and you can find logs at /report/log/index.php. The default Moodle events are used to create log entries.