In both cases, when the search engine comes into contact with the site to index it, it establishes its main theme and autonomously decides which of the Latest Mailing Database two similar pages is more exhaustive and, therefore, attributes a canonical URL to it . This process affects rankings, because Google's crawler will often analyze the page it has attributed the canonical URL charge and will spend much less time crawling the content it sees as duplicate . Deciding which is the best content to show to a user who types a query and focusing resources on the main web page, ignoring those copied from it, is completely normal for an algorithm that has to give valuable answers and rationalize the crawl budget .
Google cannot analyze all the URLs present on the internet, because they are too numerous and would involve an enormous effort which would not benefit either the company or the user who uses its services. Analyzing, classifying, following the evolution of a page involves work and money, for this reason the search engine pays attention to canonical URLs and only makes sporadic visits to pages it considers duplicates. Rel Canonical: why should you use it? If Google does everything then why should I use rel canonical? It is a question that could come to mind discovering that the search engine automatically puts the canonical stamp on a web page and takes it into consideration, leaving out similar ones. However, problems could arise by letting the algorithm choose between one page or another to show to users. The right question to ask is: am I sure that Google considers the URL that I would like to position in the SERP canonical ? I understand having faith in the evolution of algorithms, but I think it's always better to use the rel canonical to accurately indicate to the search engine the page I want to be taken into consideration and, possibly, positioned in the top positions of the SERP.