Feeds are read by many to gather your content as it evolves.
This feature makes use of the , which allows you to create very specific feeds (i.e. a given number of items, specific page type, date based limitations, etc.), and the with specific XSL files that transform the data to an Atom or RSS feed. We can support all the different formats available for feeds. We already support RSS 2.0 and Atom 1.0.
A page may be given an extra text area to enter exactly what you want to appear in the feed about this post, instead of just the default page teaser, including an image or other media. This is particularly useful if you can enter an ad for a product or service or event that you are currently promoting.
Some Guidelines for RSS Feeds: http://www.feedforall.com/etiquette-for-feeds.htm
Make 100% sure that all the links appearing in the feed are all full links (i.e. no local links because many systems will not use those local links properly. Drupal does it wrong, Squidoo does it wrong, it is likely that a very large percent of readers do it wrong...)
Allow for an easy way to see what the feed content is without sending people to the actual Atom or RSS feed itself (which works with FireFox, but not with I.E. and Safari.) Plus, if we send people to an HTML page, it can include all the edit features you can imagine and thus allows for very easy tweaking of the feed.
Although I do not really like aggregators, it is especially bad for Search Engine Optimization because it duplicates content which should not be duplicated (as per Google's own recommendations...), it still has its uses.
One example for the use of an aggregator is to collect data from many other sites without having to go on those sites. That can be useful for an administrator who wants to know whether there is a need to go on a site without actually having to visit that site. (i.e. you get information to check and then hide/delete.) The administrator can then choose to go to the site to do some administration as required.
This can work with comments as well as pages. Really anything that can be added to a public feed. Internally, we can of course offer similar features without the use of a public feed (especially for comments!)