As far as the muscles in the back go (arm muscles are the same for both basically), I've always considered a traditional grip (palms facing in) with hand close together as hitting more mid-back areas (traps/rhoms), and a wide grip palms facing away as hitting more of your lats.
There is some overlap and of course some of your rear delts get hit too. As someone has mentioned before on this board whatever your grip or width, they tend to be a
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