Swatches 8 and 9 feature twisted decreases which are meant to be a little more visible and decorative than the usual decreases. I honestly don't think I would use them anywhere. I prefer decreases to be as inconspicuous as possible.
Swatch 9 - Twisted Decreases (Full Fashioned)
The central double decrease is most commonly used at the centre of a V-neckline, or in lace patterns.