Site speed is one of the major considerations out of the over 200 Google algorythm factors. Like many SEO factors, site speed aligns with what your users want as well. Nobody wants to wait for a site to load. Google knows this and will avoid ranking slow loading sites. So when sites are optimized for speed, everybody wins.
Sometimes it takes a fundamental rethink of your content to improve speed. But you don’t have to sacrifice quality of content to get results. Any site can be optimized to load quickly, usually be addressing a number of common pitfalls.