Many many years ago I started as a junior employee in a big company together with a close friend. I was in finance, she was in HR. From time to time we had a drink to catch up and while I was doing unglamorous grunt work she was dealing with things like compensation packages for VPs, a short-list for a new regional CEO, the yearly ranking of all employees, etc. From time to time she gave me morsels of confidential information (like the salary a VP was getting or where they were planning to move the offices).It was a totally different ball game. That's why (among other things) it is very very unwise to cross off or even to confess stuff to HR, they are at a different level.

A petty thing I noticed with the years is that in HR, even very junior people will treat you with condescension and a sort of disdain. They know your salary and know where you were in the corporate ladder,they deal with the CEO packages so you are just a mediocre fish in the pond for them.

Skillful HR people also create a pretty solid network so if they leave the company they usually land sweet gigs in other companies or they can start a consulting agency. Out all the places of a corporation HR must be one of the best to be. (Cue hundreds of actual HR managers refuting me)