At my previous job I thought the same thing. They didn't stop people being bullied by superiors and basically did nothing but exit interviews and layoffs. The entire company was really dysfunctional. At my current job HR is _supremely_ competent. The entire organization is more functional and a joy to work for. I think there are subtle but significant effects when people know that it is not okay to behave in a bullying or discriminatory manner because HR takes those things seriously.