I have a website that I work on from time to time that gets pretty steady traffic from search engines. Here are some of the benefits of using SEO that I have found out about through utilizing it.
You can reach a much wider audience. When you put a website up, search engines aren't just going to rank you well for no reason. You can't expect that if you build it, people will come. Instead, you have to make it easy for a search engine to crawl your page with their software, and to rank your site according to what their algorithm needs the site to have in place.
One example of a benefit of SEO is to think about how easy it would be to sell a product through it if you were to rank well when people were searching for a place to buy something. For instance, if you sell tools then you could make a page with the keyword "tools in city name" where city name is where you're located. Then you just have to create content for that page that mentions that keyword combination a couple of times depending on how much text there is. Keyword density used to be very important, but these days it's more or less about having good content that's up to date.
Through SEO tactics, you will learn that creating a sitemap can help you to not have to do as much work when you want a search engine to index all of your pages. A sitemap can be seen as an index for your website that contains a link to each page. With plugins or some software options, you can easily have a sitemap built that you can then submit to places like Google through their submission page. Remember, as you update your website you need to update your sitemap and you also need a link to it on every page so that if a search engine's crawler software lands somewhere random it can go through all of your website.
All in all when you use SEO and make sure that you put the right methods into place, you can boost business, generate far more interest in your website, and can be sure you're not wasting your time and money on building your website.
1 - http://www.hobo-web.co.uk/keyword-density-seo-myth/
2 - https://support.google.com/sites/answer/100283?hl=en