I'd say that if you divide a long page into small chunks(may be for more Ad revenue), which actually should have been single page then using prev/next attributes give clear signal to the search engines about the main page so that the search engines can show the main page in the SERPs and attach less significance to chunks.
About duplicate content, we should always strive to reduce duplicate content and prev/next does not relate to Duplicate content. Either we should add rel=canonical or block duplicate pages altogether thru Robots.txt or meta noindex exclusion.
