SEO is important because has the ability grow your business organically and increase its authority seamlessly online and offline.
A well optimized site goes beyond ranking for keywords on search engine results pages. A well optimized site delivers its visitors with the information they are looking for to make a purchasing decision, keeping them on your site longer and sending signals to Google and other search engines that your website matches the users search intent and should continue to rank well in search results.
As for website owners, SEO is important because search engines have the best ability to send high quality traffic to your website. High quality traffic from search engines will positively impact the number of leads and sales you receive to grow your business.