Asif Anwar is a Search, Social, & Internet Marketing Consultant/Specialist working in Bangladesh (In Indian Subcontinent aka South Asia). Professionally consulting and helping small businesses on Search Engine Optimization (SEO) since 2003 and actively learning about Search Marketing trends from 2001. Passionate about SEM (Search Engine Marketing), SMM (Social Media Marketing), and PPC (Pay Per Click).
Sites evolve a lot after it has been created. Even if the contents and themes are same for the site, they throw away the old bottle and take on a new bottle. But, with the old bottle, sometime the webmasters don’t know that they are throwing away precious old wine of the link juice. Even, many SEO experts and webmasters forget what they are throwing away and go for short-term solutions.
Not all sites goes for CMS at first. The common evolution pattern is from Plain HTML site to Animated Flash site and then to Content Management System (CMS) site. For some sites, the evolution pattern can be quite complex. Each time while changing, most site owners and webmasters rarely bother about redirecting old links to the right and very relevant link or page. While doing that, they are harming the visitors, hence their business potential, and also the search engines.
Like rel=”nofollow” URL tag, a new rel Tag (canonical) has been introduced and currently being supported by major search engine to tell the search engines that the specific URL is the duplicate.
<link rel="canonical" href="http://www.example.com/printed-version.html">
This tag makes the webmasters free from relying with server end 301 redirect management, since this URL tag will be work as same as 301 redirects. And this can help retain the Authority of the home or any other page by disregarding pages that support session IDs, affiliate versions, printed, pdf versions, etc. that create duplicates of the original page.
More FAQ on this is on SEOMoz.
See what Matt Cutts, the Web Spam Head in Google has to say about it: