The immense convenience of the RSS reader in its "Favorites" tab is the reason I still use IE.
Basically, for websites with frequently updated content (blogs or webcomics, mainly), RSS feeds become updated with this new content every time the site updates. You subscribe to the RSS feed for the site, and it keeps a link to the RSS page for that site in your reader. Whenever the feed updates, the link becomes bold. That way you can easily see which sites you have RSS subscriptions for have updated, and don't have to worry about checking periodically or remembering update schedules, which is especially nice if there are a lot of webcomics and blogs that you follow. The feed links refresh periodically, but they won't be completely up-to-date all the time. The reader in the IE Favorites tab let's you right click and choose "Refresh All" to get around this. It takes several seconds, but you'll have all the feeds updated right then.
To sum up, it's like bookmarks, but kept separately, and they indicate whenever the sites they link to have new content.
