No need, if you have good content and keywords, spiders will crawl your site. I've never submitted sites in ages.. Also: if you have the link of your site (wanting to be indexed) by another site, it'll make the process quicker. SEO is necessary for web promotion
If there are links to the site on other sites that are re-indexed frequently, submitting to search engines is not necessary. However, if you don't have many links it submitting can get your site indexed in some search engines more quickly.