Render a Starship Shield Impact - Blender 2.5 - page 47

The passes other than Combined and Z won't be used explicitly in the
composiing setup; the reason to enable them is just to have the possibility to
inspect more closely a certain component of the image at any moment while
working on the composiing setup.
To finish the renderlayers setup, make sure that layers 1, 2, 3, and 4 are enabled in the
Scene butons grid (to the let-hand side of the Layer butons) in any of the renderlayers—
it's a shared seing between all the renderlayers.