Human Resources doesn't advocate for you at all. If you have any issue with insurance, they won't even go to bat for you or at least say they'll look into it. I always get the same thing with every issue : "My hands are tied."
Human resources takes a long time, and many attempts just to update your personal information. After changing addresses, it took almost two years, and repeated emails and calls just to get address information changed. With that said, I never received important documentation, including employee handbooks and insurance information.
Some employees have had insurance get cancelled on them without any heads up. The policies on insurance seem to change every year.
Career opportunities are kind of nebulous. Even when you reach out to other people, no one seems to know how to apply for, or how to prepare for other positions in the company.