If used correctly, Rel=Canonical tag can hinder Google from using pages with duplicate content as a factor when ranking a website. This means that the pages duplicate content will not be indexed by the search engine spiders. MediaOne, a leading SEO company operating in Singapore says: if you do not canonicalize your URLs, Google is liable to think that your different URLs: http://, https://, http://www. https://www. etc are different websites canibalising each other in terms of content, keywords and ranking factors. So its better to set your .htacess file to list your different URL forms to “collapse” them into 1 primary nominated URL.