What threats would allowing Jailed Shell SSH access create?

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http://forums.cpanel.net – If some of webserver clients are more of a developer kind and love to use SSH even though Im having second thoughts about allowing SSH access at all. If I would allow SSH Jailed Shell to all my webserver clients. What can actually happen? How to monitor them and are there any possible way to limit commands they use? eg. I dont want them to run gameservers on webserver. Or start Ventrilo or Teamspeak server just because they have Shell access. So how would it be safe to allow it? (HowTos)