The reason why SEO is important for business is simple: it increases the visibility of your brand in organic search engine results, which is exactly where people are looking for products and services.
If your website content is not search engine optimised and then when people search for things relevant to you; the search engine does not throw up your website as a probable solution to direct people to your site.
Investing in a SEO audit will give you the tools you need to help optimise your website and put you on the right path to help your business grow.