Carrara already renders out object outlines (Object Index layer) and Dispance to camera (Depth layer), but when saved into the single photoshop file, they become channels/masks, not layers. So if you need them and Elements don't work with those(I don't use Elements, so I don't know), just render them as external (not embedded) layers and then reintroduce them back from inside your Photoshop.

I use the depth channel all the tame for adding DOF in post using Photoshop Lens Blur (I don't know whether Elements has it).

I also use the separate reflections layer to adjust intensity of and/or blur reflections.

Same with glow. I don't like how carrara handles rendering glow effects, so I just render glow as a separate layer then duplicate it, blur it and get instant atmospheric glow around all the objects which had glow in the shaders.

There are many more uses. These are the ones I use almost all the time, so they are the ones which came to mind first.