Fun with Sprites – Sky Defense - Cocos2d-x by Example Beginner's Guide - page 107

So for example, when we later add three sprites showing the trees.png sprite
frame, we add them on top of all previous sprites using the highest value for z that
we find in the enumerated list, which is kForeground .
Note
Why go through the trouble of tiling the images and not using one large image instead, or
combining some of them with the background image? Because I wanted to include the
greatest number of images possible inside the one sprite sheet, and have that sprite sheet
to be as small as possible, to illustrate all the clever ways you can use and optimize sprite
sheets. This is not necessary in this particular game.