There are two modes of thought when it comes to offering content in a syndicated feed.
Excerpts or Summary
An excerpt feed is one that offers a few sentences about a post, but doesn't give the whole post away. Note that there is a significant difference between an excerpt, which is usually just the first few lines of a longer post, and a summary, which is a carefully crafted version that lets a reader understand it in shorter chunks.
Full Post
This type of feed is fairly descriptive. It offers the whole post in syndication, so a visitor doesn't have to leave their News reader to view the post. This is by far the preferred version by readers, since it allows for centralized reading. The Atom feed standard allows for a summary to coexist along with a full post and some RSS reading applications take advantage of this.
Read More...
The use of the more... tag is another aspect of rss to consider. More... can be useful for trimming a long post down to a more respectable size when listed on an index page, but will also shorten the post in RSS. It can be disorienting for RSS readers used to see a non-full post, so use this option carefully.