Because displaying relevant RSS feeds on your pages gives you more information about your topic that rotates and changes automatically. When used in conjunction with your own content, it can help your search rankings.
The search engines love relevant content on a website, and they like fresh new content even more. By supplementing your existing website with RSS feeds from relevant industries, you are giving people more information about your chosen page topic, and you’re giving the search engines what they want to see, which is fresh new info.
fresh content = more frequent spidering = newer cache dates = higher rankings