They are on your side if you are on the company's side. E.g. sorting out equipment issues, leave requests, forms, etc. If the on-boarding process is little to non-existent, the HR might be someone who takes care of you during the first couple of weeks until you get your wheels turning.
Frankly I'd trust the government more than I'd trust an HR rep. At least in the government you have people who believe they work for the citizens of the US.
Well perhaps the previous administration anyways...