I'm confused at the difference between Google+ profile and brand page. I mean I get it. The brand page is for your company, but I built up some circles for my profile, and now recently launched my brand page, and now don't know what to do with it. Do you post and write things on your profile that are non-business related? Then, post and link things on your brand page that are exclusively business related?
Well in marketing terms, its better to use both. For example, if I write an article on my blog I share the link on my personal profile and my Business page.
Well, like Facebook, Google+ has also introduced brand pages. I would like to say when you have an option for a separate brand page, it is always a better option to use that brand page for your branding purpose, & use your personal profile for personal purpose. Everyone, who has you in their circle, may not like seeing your brand's advertisement on the timeline all the time.
The brand page on google+ needs more work imo. Annoying that you need a personal profile to set a business profile up. Like the OP said might aswell just use one imo. At the moment anyhow i don't see them ranking well.
Bear in mind that with the brand page you can only add other brand pages to your circles. Only when an individual adds you to their circles can you add them back. As an individual user you can add anyone to your circles. There's no reason that you can't have two pages (unless the effort required to keep them up is too much in which case I would use the brand page).
Profile page is used for personal page which is similar to facebook profile and brand page is like facebook fan page
Use a Google + for business page for products/brands. Google+ itself is for individuals. Unlike google+ profiles which Google only want you to have one of, Google + for business pages are unlimited. You can setup as many as needed with Googles blessings. Note: To get the most out of them ensure you follow Googles instructions to put a G+ for business badge on your website and link from the Google+ for business page to your normal web page. Until you do this you will not be able to rank for keywords using the brand name.