At times there are multiple URLs that link to the same content. For example on a specific e-commerce website, there could be multiple links spread out throughout the entire website that would refer to a products page.
This type of linkage is confusing to a search engine, forcing it to make a wild guess on which link is the correct one. This is where the canonical URL tag comes in, it tells the search engine which link is the true link and focuses all resources onto that link.
