Difference against default Feed display?

There is a lot of potential information exposed to views that isn't readily available to the CCK output config, which only handles fields created by CCK. See the data module: http://drupal.org/project/data for one example. More granular control over taxonomy terms is another benefit. Also, depending on what you're up to you may want fields to behave differently on different feeds. In the past I've always resolved these issues with some form of hook_nodeapi hackery or another, but this provides a more sustainable and end-user friendly approach.