When the same content appears on several URLs, it is important to direct search engines to the preferred version of the content. A business may use the same content on different pages within the same site or may make use of different URLs for a site containing the same content.
When a user searches for information that matches this content, it may be difficult for the search engine to determine the original source of the content. Using a canonical link element will suggest to search engines that a particular version of the content that should be ranked more highly than others in terms of the SEO algorithm.
How Canonical Links Work
The standard HTML protocol for using a canonical link element requires that it must be included as part of the code. Inserting it will indicate that the content of the linked page is preferable to the page containing the canonical link. This functions in a similar way to 301 redirects. In some cases, Google may rate the redirect higher than the canonical URL if the Google spider considers it fit to do so. The Google algorithm may see too many canonical links to a certain page as gratuitous link building.
The SEO benefit of using a canonical link is that every similar page containing this link counts as a link to the source page. A page with more inbound links ranks higher than others. Using 301 redirects will not add to the number of links, even though the end result is the same.