Every sizable company has a HR department. However, most people who are in management position has to perform certain HR functions. So, HR skills are essential in business. When the business is good, HR needs to do hiring and training. When the business is bad, HR needs to be involved in counselling and firing. When the business is so-so, HR needs to do all those. Whether you get hire or not, HR is always there, rather than helping you, they are trying not to hire you, unless you know your future manager directly. Otherwise, you may be very qualified, but you will not have a chance to step into the door to have an interview by someone that really matter. If you are a manager, you want to hire someone, HR always seems to be forwarding you someone that you don't want. It wasted your time to meet the wrong folks, but you still have to politely meet them, spend an hour with them though you know that he/she is not someone that you will hire after 10 minutes speaking to that person. That's my experience in my previous company.
When you have management issue with your staff, especially at the bad time. HR just wouldn't be helpful. You as a manager will need to do all the 'dirty' works, or making 'tough' decisions, and take all the bad consequences about staff issue, and the HR will probably just doing paper works and a time-wasting exit interview. That's why sometimes, I do think that HR has easy life. Their job security is not that bad, their market demand is also not that bad. They know all the interview tricks, cos they are supposed to be an expert of that. Though I'm sure HR may not be as easy as I thought they are, there must be a whole of specialties and skills that you need to be equipped with in order to be a good HR person, I just have never really met one so far.