Basically, listing to directories is usually done in an effort to artificially boost a web site's link popularity. Deploying this deception is in hopes that gaining link points will assist in the overall promotion of a web site from attaining targeted traffic across the search engine results pages.
Essentially most Internet marketing plans that focus on "easy to get" link building schemes prove to have substandard content and cannot within their own power rank highly in keyphrase competitions.
That is why I find the vast majority of today's link building schemes to be not only ineffective but practically of no real value to neither the web site owner, the search engine nor the odd Internet visitor that stumbles across the page.
Rather that build links in any manner, most web site developers should stay focused on content development and making the best use of the web page's optimizable components.
How did you know what is good and bad directory base on your experienced can you explain it much further? thanks..
Every industry has one or two authoritative directories that actually serve a purpose for Internet visitors, all else are garbage dumpster directories that have self-serving marketing agendas (monetized webpages, selling links, affiliate banner marketing etc.) and they don't really add any new value to the Internet. The search engines do recognize these dumpsters but definetely devalue their lengthy lists of the desperately seeking link builders who seek to get their web site links listed anywhere, anyway, anyhow.
Now, some would argue that the DMOZ directory and the Yahoo directory are still important places to get a listing but I'm not convinced that they offer much of an SEO advantage anymore as I rarely see Google acknowledge DMOZ or Yahoo directory in a web page's backlinks.