Usually you just place at high indexed pages@active Yahoo spiders and will be indexed automatically. However it does not hurt to submit to Yahoo. You can also submit to google and Live. Others can just ignore. 0 traffic..lol..
Many of the top seo experts don't recommend spending time submitting to search engines. If you get a bunch of links from quality sites, the search engines should find your site on their own.
Unlike google, Yahoo, has free and paid submission, so for the free one takes some time to see a result. If you are fan of Yahoo, you can submit also a sitemap that has a special format ( textfile ).
If you build a few high quality backlinks your site will be crawled by yahoo, you can also submit a sitemap to your site through yahoo explorer.
I never submitted my site to yahoo but it already has more than 130 back links strange how was this possible ? I think you must have a nice visitors rate and contents and yahoo will automatically put your site in their directory.
off course yahoo will crawl your site someday if its has some good contents and rush on your site, but its always good to send your site to search engine's for indexing fast in there database.