When used properly SEO can give a massive boost to the relevance of a website. When a site is poorly optimized for search engine, it becomes increasingly hard for the search engine to list that website even if the search query is related to the content or services provided by the website. It all starts where Google or any other search engine for that matter rank website regarding usefulness or relevance to the user.
Search engines read through the entirety of the content on a website to determine its relevance. The keywords present in the content is the deciding factor when it comes to ranking them. Also, a great amount of emphasis is given to original and unique contents. If the content you post is a spin-off version or if it’s highly plagiarized, then the search engines will de-index the site and regard it as irrelevant. That is why the emphasis is given to original content when posting it online, spinning off contents will surely render your website irrelevant