In the first post of the thread that RenatoPhoto provided a link to, pay very special attention to the text "This flag cannot be undone yet so may want to read here first" under the heading "SPECIAL CASES". It means that if you enable raw capabilities on your 5D3, there is currently no way to restore your camera to the state it was in before. (In my view this message ought to be displayed much more prominently than it is, and in more places.)