Without SEO, a website can be invisible to search engines. A good webmaster will be able to use SEO in a way that allows search engines to find clues that will help the engines understand content. SEO allows you to have a website that is formatted and annotated in a way that search engines can digest. This is your best chance to be one of the top suggestions on search engine results pages.
SEO can help make your business website work to get you a higher market share. The vast majority of customers check online reviews before making a purchase. When people find what they want after a search, they are more likely to promote your business on social media. Without SEO, customers will have a hard time finding you, and may easily find your competitors.