How rel="next" and rel="prev" helps in SEO, if used for pagination? Is it really required ?
i.e. imagine you're on page 2:
<link rel="prev" href="http://www.example.com/article-part1.html">
<link rel="next" href="http://www.example.com/article-part3.html">
Pagination with rel=“next” and rel=“prev”
Much like rel=”canonical” acts a strong hint for duplicate content, you can now use the HTML link elements rel=”next” and rel=”prev” to indicate the relationship between component URLs in a paginated series. Throughout the web, a paginated series of content may take many shapes—it can be an article divided into several component pages, or a product category with items spread across several pages, or a forum thread divided into a sequence of URLs. Now, if you choose to include rel=”next” and rel=”prev” markup on the component pages within a series, you’re giving Google a strong hint
Is it required? No. Should you do this? Yup, it'll decrease the 'duplicate page' penalty because it can see that it's a next/prev page of the current page. It indicates the relation between pages (Hence rel).
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.
AFAIK it will help you to avoid duplicate content issues only, because paginated pages have the same title and descriptions, to avoid this behavior Google introduce this tags. Instead of manually applying this tags, I usually block the paginated pages in ROBOT.txt file to avoid the duplications and this is the easiest method when compared to the rel method because you need to mention manually everywhere and those tags are not required if you block the paginated pages in ROBOT.txt.
