The RAW file is the 12-bit per colour per pixel image as it came out of the camera sensor, plus individual adjustments that have been made. When you modify the ajustments you are only working on the adjustment itself, not the basic signal. You can always go back later and change it.Originally Posted by boomtap
The JPG is the final compressed 8-bit per colour per pixel image. Not only have you less data than with RAW, any changes are permanent and cannot be undone.
For example, imagine you convert an image to black & white, then the week after you decide you preferred the colour version better. In RAW you just undo the change that gave you black and white and hey presto you have a colour image again. In JPG when it's gone it's gone.
Personally I only use the camera manufacturer's tools to work on RAW. I have seen several tests where Photoshop does a worse conversion than the dedicated converted.
Charles