Search engine optimization is often seen as a good way to keep away from costs on advertising by attaining high rankings in the natural search engine results. Not only is this not the true function of search engine optimization, it can, in fact, be a unsafe way to conduct business.
Search engine optimization should never be the sole means of marketing any business, since search engine algorithms are in constant flux, and any one of day by day changes can impact a website's ranking negatively, to a point where the entire business can be put in danger. So natural rankings should never be the single source of traffic for any website that is being run as a business. With that said, search engine optimization can contribute deeply to almost any online marketing campaign.
As mentioned above, search engine optimization is not appropriate for those who are looking to save money by getting away from other forms of online marketing. SEO is a long-term method, particularly if it is to contribute in a fashion to the bottom line of an online marketing effort. It is a mid- to long-term solution which does require a significant investment of time and wealth. So if you have just started an online business (or something with an online component) and are looking a path to jumpstart your website traffic than search engine optimization is not suitable for you.