This example 480x360 is from a 1600x1200 render and is in PSD 7 file format.

The Layers contain refraction, reflection, shadow, specular, diffuse and background. Channels are alpha, depth, view normal, shadow, normal x, normal y, normal z.

 Download and see the time saving that can be achieved with this type of prepared file.

You may have to R-click and save target as.