Pagination, the practice of segmenting links to content on multiple pages, affects two critical elements of search engine accessibility.
Crawl Depth: Best practices demand that the search engine spiders reach content-rich pages in as few "clicks" as possible (turns out, users like this, too). This also impacts calculations like Google's PageRank (or Bing's StaticRank), which determine the raw popularity of a URL and are an element of the overall algorithmic ranking system.
Duplicate Content: Search engines take duplication very seriously and attempt to show only a single URL that contains any given piece of content. When pagination is implemented improperly, it can cause duplicate content problems, both for individual articles and the landing pages that allow browsing access to them.