I have seen the negative effects of URL Canonicalization in action. Have you?
“Canonicalization is the process of picking the best url when there are several choices, and it usually refers to home pages.”
“In computer science, canonicalization (abbreviated c14n, where 14 represents the number of letters between the C and the N) is a process for converting data that has more than one possible representation into a “standard” canonical representation.”
“In information technology, canonicalization (pronounced KA-nahn-nihk-uhl-ih-ZAY-shun and sometimes spelled canonicalisation) is the process of making something canonical — that is, in conformance with some specification.”
“If the search engines sees a page as being published at many separate URLs, the search engine may rank your pages lower than they would otherwise, or not rank them at all. Canonicalization issues can split link juice between pages if people link to variants of the URL.
“The practice of consolidating all versions of a page under one URL is referred to as “canonicalization” (because you collapse all versions under the “canonical” or true version). By adhering to several best practices, you should be able to address 90% of common site-wide canonicalization issues on your site and consequently increase how your site ranks.”
“Your website can be accessed with www.domain.com and domain.com. Since Google penalizes this due to duplicated content reasons, you have to stick your domain to either www.domain.com or domain.com. But – since some links are outside of your website scope and the search engines already have indexed your website under both addresses, you can’t change that easily.”