Both MT and WP offer a feed which can be set to a full feed or just an excerpt. Blogger who rely on ad revenues will generally choose just an excerpt, while bloggers who are more focused on getting their stuff read will offer a full feed. Then there are the other 99% of bloggers who don’t know what feeds are.
For those, let me give a quick explination. The feed would be the bare-bones info of your blog. The title, author and text (exeprpt or full) that in in a format easy to process by scripts. At my site http://new.elevenoclock.comI use the feeds provided by many news sources as well as blogs to display the current headlines. News readers like Eleven O’clock News, Google Reader (http://google.com/reader ), and http://BlogLines.com use the feed from your blog to show the content to others. If you just like people reading your stuff, then that would be okay. But if you want people to go to your site, then you’d offer only an excerpt so to finish the article they’d need to come to your site.
One of the most important things about feeds, if you want people to use them, is to make them handy, and display the link to your feed somewhere where it’s easy to find. Typically it’s either at the top or the bottom of the page, but sometimes it’ll be in the sidebar. It’s also, typically, included in the header of the page so scripts can pick the link up there.
Some blogs (and online newspapers) have gone even further than limiting the content, and insert ads into the feeds themselves. That’s perhaps a bit stingy, especially if you’re only offering an excerpt to begin with, but it’s what they choose to do.