There are several publishers of RSS feeds that are specific to a particular theme. Since the feed is highly targeted, it could contain several keywords that you want to rank highly for. Adding these keywords to your pages helps Google tag your site as one with relevant content.
RSS feeds from large publishers are updated at specific intervals. When the publisher adds a new article to the feed, the oldest article is dropped.These changes are immediately effected on your pages with the RSS feed as well. So you have fresh relevant content for your visitors every hour or day.
3. RSS Feeds Result in More Frequent Spidering
One thing I never anticipated would happen as a result of adding an RSS feed to my site was that the Googlebot visited my site almost daily. To the Googlebot, my page that had the RSS feed incorporated into it was as good as a page that was being updated daily, and in its judgement, was a page that was worth visiting daily. What this means to you, is that you will have your site being indexed more frequently by the Googlebot and so any new pages that you add to your site will be picked up much faster than your competitors.