Following on from a response to the question Force www. on multi domain site and retain http or https - I was wondering if SEO (specifically, avoiding duplicate content penalties) was the only reason for forcing the www. (or vice versa, if you prefer).

Are there any other reasons why an authoritative domain name/convention would be desirable?

3 Answers 3


Is (was) SEO the only reason to force the www. on domain names?


Are there any other reasons why an authoritative domain name/convention would be desirable?

Run Google's Page Speed - if you are serving cookies under the root domain (i.e. example.com) you will find that those cookies (per RFC 2109) are being sent as part of every HTTP request, including requests on static content served under subdomains.

Instructing clients to send spurious cookie data on every request is a sub-optimal solution - if you want to see the fastest possible turnaround on client requests, it pays to restrict cookie usage to a subdomain (i.e. "www.example.com") and put your static content on a separate subdomain.

See the Page Speed Web Performance Best Practices document for further suggestions in this vein.


For some kinds of CDN or global load balancing, you need to create a CNAME for the domain name you're using -- and you can't CNAME your main domain, so you need to use a subdomain. Even if youre not doing this now, if you think you might want to do this in future, it's as well to set it up now so that you don't have to change it later.


SEO is nothing more then usability, accessibility, semantic mark up, and quality content. Forcing the www falls under usability. By forcing the www you have consistent URLs which is good for users as they can become confused when they see two URLs that are similar but they know are different.

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