There's policy, and then there's real life. Users often make inappropriate requests from the help desk and its techs. Look out for these big ones, and make sure that your support staff is prepared to refuse them.
One problem with running a service-oriented help desk is that people keep coming to you for help.
OK, that's meant mostly as a joke. Mostly. In my experience I've found that creating strong relationships with one's clients will lead to more service calls. It has something to do with inhibition and intimidation. If customers have a positive experience with a tech, they'll feel reassured about the support process, and this will make them more inclined to ask for assistance in the future.
Creating comfortable clients is ideal for a freelance or contract technician, who gets paid by the call or by the hour. Every service request is money in one's pocket. Comfortable clients can be less ideal for a standing in-house support team, though. Users' inhibitions can become so low that they start asking the help desk to provide support that's outside appropriate boundaries. This is especially likely in environments that don't impose any checks on the urge to file a support request, like fees, departmental charge-backs, or ticket accounting.
Responsible IT departments should have published policies about what they'll support. Even if those policies are out there, though, that won't keep techs from getting requests for assistance that are beyond the help desk's authority. Being aware of the types of inappropriate—and sometimes informal—support requests will let you anticipate them and will let you prepare your techs to handle such things, if and when they appear.
Those are the three types of inappropriate inquiries I see most often as an office support tech. If you have any others to offer, let me know in the comments.