Why doorway pages used?

[Jackandrew]

I heard that doorway pages are very useful to get ranking in less time. Is that true? Should I use them? Please guide me.

[dennis123]

Doorway pages are a group of low quality pages which is developed to promote a particular keyword and which have no relevant content or may have duplicate content. These low quality pages will redirect you to a different page of a website which the webmaster feel is the most important. It is a black hat seo technique.

[RH-Calvin]

Doorway pages are web pages that are created for spamdexing. This is for spamming the index of a search engine by inserting results for particular phrases with the purpose of sending visitors to a different page.