Okay, I'm sorry, but this is a silly question. A blog can play any number of roles to a brand. It could be the face of the company, it could be used for marketing, for notifying customers of what you are doing, etc. It can be a news outlet, publications, it could be ANYTHING.
What you need to take away from this rant, is that if you launch a blog and you don't know what it is for. You are already going to fail with it! A company should know what it wants the blog to provide for the company before it even launches it. If it doesn't do that, how do you verify it is performing to your expectations? How do you know if you need to shift your strategy? How do you measure its usefulness to the company and to the target audience?
As an aside for everyone else, unless you are going to detail your story about how you utilized your blog to play an important role in your brand/company, your post will be treated as fluff. No more of this one sentence non-sense that isn't even useful.