RSS

This is a very google'able question that might do a better job than me but I'll take a stab at it.

RSS stand for Really Simple Syndication (which I suppose the really simple part is over estimated) and I believe all web browsers as well as most email clients provide ways to Subscribe to RSS feeds as well as dedicated RSS readers (though I don't know anyone who uses one). So this feed follows a standardized format that is easy for seo bots to scrub and view content of your blog post thus helping to create more visibility. There are a number of factors that come into what bots are looking for but this is a light explanation. Beyond increasing search engine visibility, the RSS feature allows for a way for users to subscribe to a given blog, and not have to physically come back to the url to read an update or new post.

If the topic of the blog is vital to know about but posts are infrequent, such as software updates, weather emergencies, or even deal watching a user may benefit by subscribing to the rss feed in a set and forget kind of fashion.