We usually recommend that our clients avoid launching their blog under a separate domain name / URL from their primary brand website. The reasons are both related to branding (brand affinity) and search engine optimization (SEO). While this general recommendation remains, with Google’s recent announcement about link treatments, brands can now add some subtle branding structures and URL treatments for their blogs while still maintaining SEO value to their core domain.
Matt Boynton and Laurent Magloire from the Revenue Architects team point out that Google recently announced that sub-domains and domains are going to be treated equally. So blog.brand.com and brand.com/blog will both maintain the same SEO value. Prior to this announcement, blog.brand.com would have been treated as a separate domains and brand.com would not have received the SEO value of incoming links to blog.brand.com.
We will still suggest that to maintain SEO value and brand affinity, you should not create a separate domain for the brand blog (i.e. do not create something called brandblog.com), but now you can make some additional choices for how to brand your blog and structure your blog domain name. Here is the article.