Some years ago there are just a few directory in this world. Some big directory are dmoz and yahoo. People raced to submit their website into the directories and hoping get more visitor. For that time submitting your site into directories is must to be done.
But now there are many directory exist in this world. Everyday new directory appears on internet. If the directory is new your site can be approved quickly. But after some while many site has been submitted into the directory and you must wait for some weeks maybe month to can be approved.
Except that you can expect more visitor form the directory. Remember people usually use search engine to search something. They rarely visit directory.
If you want earn visitor quickly so you must forget about submitting into directory. But if you want get backlink (to increase your positions on search engine) you can do that. But find do follow directory so you can be indexed.
Sometimes I submitted my site into directory that I know give me fast approval to be listed. And the directory is do follow.