Never forget that, while most of your traffic will be coming from the search engines, whatever traffic you get from a well-maintained web directory will be targeted traffic. These visitors are far more likely to be people who are looking for what you've got.
Relevant category is also matters in directory submission. Also Google has now not giving it so much preference but high PR directories are still good.
Directory Submission is very important in seo because you get more backlinks and that means more traffic to your website and also your site get indexed faster.
Here is a relevant link for all of those who want the perfect answer and reading this thread... www(dot)manual-submissions(dot)com/directory/tutorial/what-are-the-main-benefits-of-directory-submission(dot)php...