One important thing if you are building a RSS application is that the server should support conditional requests (the If-Modified-Since header). This way, a client does not have to download the entire feed on every update. It simply sends the last update date with its request and the server returns an empty response if the feed is up to date.

There are some applications (for example YouTube) which dont support this, resulting in higher-than-necessery data usage, especially on mobile.