Too Long; Didn't Read
If a single page can be reached through many URLs, Google will treat them as duplicates of the same page and will choose only one URL as the canonical one to be indexed. Google will either pick the URL for you or consider both URLs to be equal. This might result in a substantially lower rank in search results. Even worse, the search engine may pick the incorrect page as the original, displaying outdated content. WordPress uses the “[redirect_canonical()] function, which is intended to prevent duplicate content penalty.