TOPIC: Blogging, the why of it?

As I understand it a blog brings people and or spiders back to a website thus generating numbers of visits affecting rankings etc. I note most blogs on inspector sites have to do with building and inspecting, but not all. Some chose to write on other topics that interest them and may interest others, like the navy for instance. I am wondering about the strategys behind the choices of content within the blogs.
  Are they just what you like to write about? Do you think a person who is looking for an inspection will revisit to get home repair tips after buying a home rather than visit a diy site?
  If blog content is designed to get readers back to your site how does that translate into jobs? Or is the blog solely to increase ranking on search engines?
  If a blog were to contain content other than that relating to home inspection but drew many visits would the search engines "count" the blog as being relevant to the site or would they deem it relevant to whatever the content was about?  What do you think? 

The search engines count a visit as a visit, so any increase in traffic is good. Obviously writing on HI related topics is best as it increases your site relevancy for HI searches, but blogging on other topics has its advantages as well. For example some guys blog so much and so well that agents and clients subscribe to their blogs and see the updates daily on their system. This brings people back to their site continuously. Also, even if you're not blogging on an HI related topic, you might be getting your city names in there which helps.