It's perfect for removing short events that don't belong (like a passing truck with no muffler, or a cough from the audience, or string squeaks from a guitar, for example). As BenK mentioned, there are a number of creative ways to use it too.
It's a complex tool, but very powerful. I recommend checking out the Kenny Goia video tutorial on using it effectively.
http://reaper.fm/videos.php#vSBO_VC9q3E