What jobs run for cron.php? How can I automate files:scan?

What types of cleanup jobs are invoked when cron.php is ran? How/where are they defined? I would like to automate a files:scan operation (I know how to do this using crontab) but I thought I read that this should be part of cron.php, and if so, didn’t want to have it run twice if not needed. What exactly happens or is ran with cron.php? Thanks.