You set up a site for a client and after launch, they complain because important things are not happening. Search is not being updated. Backups aren’t being run. Boost is not being cleared. Logs are not being pruned. All these things should run automatically when cron is run (Drupal comes with the ability to run cron automatically) at specified intervals, such as every 3 hours. So when does cron actually run, if not at the specified interval?