Subscribing to those 2 feeds will keep you up to date with everything new on this site (a mailing list is also available if you prefer less frequent updates via email newsletters).
Articles by Tag
Useful if you're only interested in certain types of articles. For instance, if you only want to be notified of updates in the "downloads" section, you can subscribe to the Updates tag RSS feed.
Comments by Article
You can follow new comments on a specific article by subscibing to its own RSS feed (availble at the end of articles).