I think the biggest difference is in rough v. finished (ie fished) work.
With the former, while having a few inches of slack isn't a bad idea, it can result in an "unworkmanlike" appearance that might peeve AHJ's during a rough inspection.
With fished, who's going to know?
Maybe the goal is to anticipate future access to the wall cavity. After all, most folks think of wire going pretty much perpendicularly out of a box.