When we go to a search engine like Google and do a search for something (a keyword), a list of sites considered relevant to answering your search is displayed, related to that keyword you entered in the field. The SEO service serves so that your website can appear at the top of that list, on the first page of Google, for example. Financially it's easy to see that by increasing your site's view on this list, your chance of getting more customers also increases. Therefore, SEO serves to increase ROI as well.