Two reasons for this:
- There are sites where the RSS/Atom feed is the only source, and when it expires the content is gone forever. This sucks!
- The insertion of adverts into RSS/Atom, as text or otherwise, is something that usually makes it past my (otherwise nearly bulletproof) set of plugins to block that stuff. I really really don't want to see adverts ever, and this would help me do that without needing to try to implement that stuff in greasemonkey. It would also hopefully let me get lots of other people doing the same thing