I don’t think its necessary to go into the benefits of adding a blog to help market your site. Its widely accepted as an easy way to add new keyword rich pages and help out rankings. There are some questions about whether an off-site blog or an on-site blog is better for rankings. When I’m referring to an on-site blog, I’m assuming its going to be integrated into the main site we’re promoting. An off-site blog might be with a blogging service like Blogger or something similar. The off-site blog will link out to the main site we’re marketing. The thinking is that that off-site blog will generate more rankings potential for the main site because it will be a valuable incoming link to the main site. While that may be true to some extent I still prefer on-site blogs.

An off-site blog may have ranking benefits by having externals links from another site into your main site but the off-site blog will require its own link building campaign independent of the main site so it can get ranked on its own. I’m not sure its a good use of resources to have 2 link building campaigns: one for the blog and one for the mian site. One benefit of an on-site blog would be that we can use the blog pages as potential landing pages for Adwords and other PPC marketing (sure we can do that with an off-site blog but it would require another click before they get to your main site). I think you could write your on-site blog posts in a way that would make the main site an informational resource for its theme. I think the SEO benefit would be better as a
result.

Keep in mind that Google hires teams of people to visit every site in their search index and rate them. The purpose is to improve the quality of search results and get spammy looking sites out of top rankings. I believe there are so many spammy looking blogs out there that just link out to other sites that their effect is decreasing over time as a result of this manual rating. The blogs like this are labeled as thin sites and devalued in ranking once they are reviewed. I think its better to focus on getting blog content on-site that makes your main site look more like an information resource. I would shy away from the traditional blog look and feel and try to make it look more like a rich resource of information about issues related to the topic. When it gets manually reviewed, you’ll more likely get a bigger thumbs up than you’d get from a thin off-site blog.

Of course this is all just an educated guess at best so take it all with a grain of salt.