Oct 02 2009
Some web designers/developers will tell you that for SEO, it's a good idea to have your blog as a separate site (i.e., on a separate, unique domain) from your main site. Their argument is often that you'll be able to pass some link juice from one to the other. While this may be true to a degree, there are reasons why that's actually not a good idea.
Separating your site and your blog ends up watering down the strength of each site. Essentially, you're doubling any SEO efforts!
Many links will go to one site and the other site only gets a portion. The other site is then missing out on link diversity and all the benefits that that brings. Additionally, you miss out on maximizing domain authority. By keeping your blog on your site (i.e., on the same domain), however, not only are maximizing your domain authority, you're also increasing the link diversity: A lot of different links to various pages, which means there's more for you to rank well for, boosting your domain authority and PageRank.
You also then have the opportunity to diversify your link anchor text and build up your internal linking. This becomes especially crucial when you're planning on adding a blog to your site.
Setting up your business blog somewhere other than your business domain means trying to pass on some of your authority to the new blog. Instead, adding the blog to the site means you've already got some authority and you're adding to the ever-important piece of the search engine ranking puzzle: content.