let me explain the difference.
call pocket
you call a cross side bank. as soon as the ball is hit it is obvious you are off by half a diamond. the object ball hits another ball and veers into the called pocket. yea you made a legal hit. yea the correct ball went into the correct pocket. but you cannot deny it was a slop shot.
call shot.
a scenario i have been faced with numerous times. due to some achohol enhanced ego and my opponents desperation to win some of his money back we are playing a hundred dollar game. big money back in the early 80' for a ditch digger. you are on the 8 ball with your opponents last ball partially blocking the pocket. its obvious the 8 will go. only question is will it go without hitting his ball or not.
a whole lot of pressure riding on your call. do you call it off his ball or do you call it clean. you call it clean and it hits his on the way in ...you lose. if you call it off his ball and it goes in clean ...you lose. how sure is your aim? how steady is your cue ? its a whole lot easier to just call the pocket and smack it in without worrying whether you hit his ball or not.
i hope you see the difference.
Sorry, again, there is no difference. As long as the ball goes in the indicated pocket it makes no difference whatsoever. I would never play this way but I don't play in bars where people do, either, and haven't for about 40+ years.