Julie is correct. When you have a blog that is associated with your website it's another opportunity for you to market you, your business and the services you have to offer is a subtle and sometimes not subtle way.
If you are looking to focus on offer HR services to small businesses then focus on topics related to HR and the issues that arise for small businesses. If your focus is supporting HR professionals, consultants and contractors then look to writing topics that are relevant to the HR professional as well as writing about tasks and services you can manage on their behalf.
By writing about topics that relate to your niche and target market it helps to affirm your expertise in the area and shows how you can become a benefit to their organization.
I actually have two blogs, one attached to my business and a second one called
Social Media Redhead - It's a mix of technology tips and just simply other things I find interesting. The cool thing with the platform I'm using (called
Posterous) I can post any relevant topics from this site to my business site.