Just that it doesn't get gross and tamped down and wet. The chickens pretty much stir it up themselves, though, with natural scratching action. (Sounds like a commercial: Now, with Natural Scratching Action!)
this is a great question since I didnt know about "stirring" the litter till about 2 months into it. Now I do it every other day, and DE it once a week, and pine shavings it every other week. Been doing it since day one and it works great!!! the stirring makes it so fluffy again and takes the smell if any right away!
Stirring helps keep it dry. I also like to throw scratch on it in winter and the chickens stir it for you. They also love to dust in it..sounds gross, but no bugs. As long as there is no moisture or smell, you're doing it right.