What are survey and polls in a website and what are the advantages?

I think there is 1 prime advantage in having surveys and polls on your website; the length of time someone stays on your site. Though search engine algorithms are secretive, I believe many big search engines use this as part of their equation when ranking sites. The length of time someone stays on your site, without bouncing back, usually shows "interest and relevance". So any tricks you can use to keep someone on your site longer I believe will help you in the long run.