I am the owner of a webhosting company that uses Fantastico and it also installs Moodle. Our servers are loaded fairly light and so we allow crons to be installed by clients provided that they are well behaved crons.
I have a client that is running "cron.php" every 15 minutes and this script is buring 30% of the total CPU every 24 hours. Even with lightly loaded servers I hope you can understand why we can not allow a single user to occuply fully 1/3 of the available CPU time.
I do not have time to dig in to Moodle and learn about it, so in the interest of providing a hosting site that is favorable to this software, I was hoping that someone here could just give me the lowdown on the cron and why it might be such a CPU hog.