Here, in a very brief nutshell, is what I've learned. If the camera's auto white balance was always perfect, I doubt many people would shoot raw, because we can adjust contrast levels etc for in camera jpg. But white balance is different. Once a picture has been converted to JPEG, with the Gamma curve imposed and each color represented by 8 bits, it is pretty much impossible to make major corrections to white balance. I know, I've tried in the past. On top of that, you get to play with black level, brightness, and noise reduction ... it's really powerful and amazing to me. But I think white balance = color temperature is the key adjustment.
So this past weekend was my wife's mother's 80th birthday and there was a celebration in her house. In that house, the kitchen is lit by cool florescent, the dining room by incandescent, and the room with the TV is lit by a floor standing lamp with warm florescent bulbs, and a yellowed shade. In short, the lighting differs dramatically. So I shot raw + jpeg, and figured I'd get my first real use (not just practice) with ACR.
It turns out the the camera did rather well with cool florescent and really well with incandescent; I didn't even bother to mess with some of the .rw2 files. But it was WAY off and inconsistent (by a couple of hundred degrees in color temperature) in the room with the warm florescent under the yellowed lampshade.
Below are two versions of one of the worst jpegs. The lamp with the yellowed shade is off to the rigt. The first version is the out of camera jpeg, the second is the ACR conversion from .rw2. Shot at ISO 800, AWB, G10 with kit lens. (The couple are friends of my wife's parents).
By the way, at ISO 800 in ACR I raised Luminance noise suppression to 35 or 40, that really got rid of the noise. Chroma noise reduction default is 25, I left that alone. I did once reduce it to 0 to see that there was indeed chroma noise; 25 gets rid of it.
