In short: RAW has more room to fix photography-errors later on.

If you make the perfect picture happen in camera, JPG is all you need. But if you used the wrong white balance, over- or underexposed a bit, had some color problems you have more headroom in RAW to fix these things than in JPG.  
Thats not to say you can't fix them in JPG, but in RAW you probably get better results.