Submitting sites to a search directory is used to get backlinks to your website. It is one of the key methods to improve the SEO of a site. The more backlinks you get, the more is the probability that the search engine will index it sooner, compared to when it is not listed. Directory submission is mostly free.
You can also enter a site title, which is different from the URL, containing your keywords. In this way, you can generate anchor text for your site. Furthermore, most of the search directories are ranked higher in the search engine result pages so if you submit your site to such directories, there will be more chances of your website receiving high page rank.