I am studying the use of sudo right now, and I would like a simple explanation of what exactly Host_Alias is used for. Reading the /etc/sudoers files does not provide too much info on this.

What does Host_Alias restrict or enable?

For example, lets say I have 6 computers, 3 of them belong to an administrators group and the other 3 belong to a faculty group. Assume they have static ip's.

By adding:
Host_Alias ADMINS = 192.168.1.1, 192.168.1.2, 192.168.1.3
Host_Alias FACULTY = 192.168.1.4, 192.168.1.5, 192.168.1.6

Then, in the user specifications I would indicate something like:
jill FACULTY = /usr/bin/, !SU, !SHELLS

From what I have been able to deduce this means, jill, when logged on to a faculty machine would get whatever commands are in /usr/bin and would not be able to su or change shells. Now, if she logged on to an admin computer she would not have these rights/restrictions correct?
Any clarifications/corrections will be much appreciated

http://www.gratisoft.us/sudo/sudoers.man.html

Edit as I think chrism01 has better answer.

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@OP: you are correct. Host_Alias doesn't 'do' anything, it's just a shorthand way of naming the systems you want to use in a particular sudoers line.
In your case, you have not specified a line for ADMINS computers, so nothing is allowed for anyone...
The sudoers files ADDs privileges; if nothing is specified, nothing is allowed; you have to read the entire file to check who is allowed what and where.

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