Originally posted by hks_kansei What does this mean, that a RAW file can't be overwritten?
When using RAW think of your RAW file as a film negative and the resulting jpeg as the same as a print. You can go back and reprocess the RAW any number of times to get a different look. Just like you can print out a negative and get a different result. Nothing you do to the RAW file actually changes any of the bits. When you edit a RAW you are just compiling a script of changes you want made when you actually export to a jpeg.
In many cases if you are exposing correctly there will be little or no difference in the result. The big difference is the ability to improve a less than perfect exposure because the RAW retains all of the bits that are tossed out when you make a jpeg. If you shoot jpeg in camera those bits are tossed as the image is 'cooked' and saved by the camera so you never have the opportunity to use them.
The camera always shoots in RAW. If you have it set to jpeg, the camera is creating the jpeg according to the script in the camera from the RAW it took. By saving the RAW you then have the opportunity to do on the computer what the camera did in a few milli-seconds. This might take hours on the computer and end up no better than what the camera did. Or it might be vastly better, it depends on the image.
Both RAW and jpeg have their place, if you are satisfied with the jpeg quality out of the camera, great, don't lose any sleep over it.