There is always the potential to mess up an image by under or over exposing the shot. One of the main reasons I suggest shooting RAW without exception is the extra capability you have to develop the file and save the shot if needed.
Of course RAW is not meant as a crutch - we all try and get it right the first time but if you do miss it - there is more data to re-process in RAW than JPEG.
Last weekend I made a shot in a church - a quick grab shot - and when I looked later in Aperture I could see I missed the exposure by over two stops. Rather than just tossing it I decided to work the file in the program and then tweak with NIK software. Here is the before and after. The exposure was ISO 400 1/60th @ F/4. I should have been at ISO 1600 probably.