I think its not a secret but its just not how HR is presented to employees. Its presented as the group where you go when you have a problems with someone. Unfortunately HR may see the person complaining as the problem if its in the companys best interest.

I have never went to HR and never will. They tend to have very fake employees in that group as well. People who act like they are friendly but they wont back you up when needed.

As a manager you have a better chance of getting what you want from HR since you are more important to the company.