Search engine optimization (SEO) is the process of improving the volume or quality of traffic to a web site from search engines via "natural" ("organic" or "algorithmic") search results. Typically, the earlier a site appears in the search results list, the more visitors it will receive from the search engine. SEO may target different kinds of search, including image search, local search, and industry-specific vertical search engines. This gives a web site web presence. (From WIKIPEDIA)
I agree some SEO, but not go extremely. Some SEO is like having chocolate, and extreme SEO is like indulging in drug you will ruin yourself at the end. If you leave hundreds of links in short time Google may give you a good position. But Google is not stupid and they will find you have too many votes from useless link tanks and cheating pages, and Google will remove you from search results. Today one my friend want me to do SEO for him because his competitor haetech do enjoy the benefits from recent jumping in Google search by paying for link tanks and cheating SEO. I told him to focus its business core, his competitor is crazy and cannot go long.