A business needs SEO when they are ready to accept visitor traffic to their site. SEO is used to improve ‘organic’ (unpaid) visitor traffic to the site. You can use ‘paid’ search but once you stop paying, you are very unlikely to continue to still see anywhere close to the same traffic if no organic SEO has been done in the meantime. White hat SEO practices are typically focused on creating the best possible experience for your visitors which will help you not only in getting unpaid organic traffic, but also keeping your visitors coming back as well.