For what I said, the reverse applies. If you're really worried about people hacking it through physical access, put it in a location where they can't easily get to it. Likewise if you can't put it in a place where people can't easily get to it, don't put important stuff on it. There's no reason that a set of computers should be restricted to a certain class. When I took unix class, at first we had to telnet to a remote Mandrake box. It was in a closet so people couldn't get to it. Then it was discovered that 3 people in the class, including me, used Linux at home, so we installed various distros on 3 computers in the classroom. And no one really cared if you touched them. Again, don't put stuff that you care about on computers in the open.Just because you can't stop people from cracking your computer doesn't mean any security precaution are worthless efforts.
Just because there is no way to completely secure intruder(s) from entering your home doesn't mean you should leave all of your doors wide open at any time.
It's all about making it harder and much longer to get access hoping that someone will notice within reasonable time.