The benefits of using subdomains to enhance SEO
There are many advantages in using sub domains (e.g. searchengineoptimising.retiarius.com is a subdomain of the retiarius.com primary domain) to enhance the ranking of the primary domain.
Google and MSN both class a subdomain as being a seperate site to that of the subdomain (see this article ).
Barry Schwartz points to a thread at Search Engine Watch Forums discussing the subject:
“Subdomains work very well at the moment. No doubt about that. I can take a prominent, old, domain, set up a brand new subdomain, add one link from the original domains front page, throw up whatever content I want and within days have plenty of traffic. These days it seems that almost all linkpop value from the original domain is transfered – and I see this happening in both MSN and Google.”
Another advantage is that sub domains are usually free to implement on commercial servers – you own the domain and therefore can apply unlimited subdomains to it.
I think that this separation of a subdomain and its primary domains by search engines will have to continue because of the free blogging sites such as blogger all issue their clients a subdomain such as yourname.blogspot.com, and as such cannot exclude subdomains from their search results because ALL the blogs on blogger are owned by seperate individuals.
By using a subdomain for a blog, and cross-linking a new primary site to it you automatically have set up some linking value to the new primary site. If the blog is sued as ‘link bait’ with articles likely to interest a lot of readers then you can increase the cross-traffic to the, probably less frequently updated, primary site.
But you must not go mad at producing endless referring subdomains because because Google has set a bar on the number of subdomains they will reference.
I would like to quote Vanessa Fox, an ex-Googler and contributor to Search Engine Land :
“Google is no longer treating subdomains (blog.widgets.com versus widgets.com) independently, instead attaching some association between them. The ranking algorithms have been tweaked so that pages from multiple subdomains have a much higher relevance bar to clear in order to be shown.”
So, with care the use of subdomains will enhance your site a low cost but don’t over-egg the pudding … it could backfire on your search engine ranking.