the point of this picture is to show the warm highlights/cool lowlights technique.
it can be vice versa, but you dont ever want warm highlights and warm lowlights or cool highlights and cool lowlights. it works best with a contrast between the two, although there are exceptions.
this is a more extreme saturated case than is needed, mind you.
say a beginning painter is trying to render something red. their first instinct is just use a saturated deep blood red and shade up to a bright saturated firetruck red. they dont take into account the cool highlights technique, or they wont even use a bouncelight at all, like the blue one here.
most of the time i use a much more desaturated (less pure) blue for such a task.