The quick help diagram is not saying something incorrect, since Shift+ NumPad 1/3 is supposed to rotate fast, but we are aware that for some reason it doesn't work well.
The F7/F8 keys do something different, they don't rotate "fast", they rotate at 15 degrees intervals, aligned with the parking original heading so, they are used when you need to quickly rotate something, like an object, to headings that are easier to align to the parking heading.