This event trigger after the cron task finished process. So with this trigger you can extend the process more after the completion of cron task.
$today = new JDate();
$message = 'Your scheduled task has been completed at ' . $today->toFormat('%Y-%m-%d %H:%M:%S');
$mailfrom = 'email@example.com';
$fromname = 'www.jomsocial.com';
$email = 'firstname.lastname@example.org';
$subject = 'Scheduled task completed.';
JUtility::sendMail($mailfrom, $fromname, $email, $subject, $message);