I find that Render layers in Blender/Cycles render are a very useful tool for creating any kind of Render passes or AOV’s needed for compositing.
You can easily create render passes with different material overrides, or use the ability to exclude scene layers to create render passes with different light sources or different geometry.
For instance, there’s no built in World Position AOV in Blender but it’s really easy to create one using a Render layer with a World Position shader override (a world position shader can be created using an ‘Input > Geometry’ node)
Or in another case,
I thought you couldn’t have a decent AO render pass (using one scene file) because the AO shader doesn’t have a distance parameter and the Environment AO (that does have a distance parameter) produces a fake GI effect that I don’t want to have in the beauty-pass,
But using render layers it’s actually pretty easy to do because a render layer can be set to not use the environment or not use AO.
Bottom line, the Render layers feature in Blender gives you huge flexibility in creating custom output images or sequences out of a single scene in a single render job (not a single render because each render layer is rendered separately).
On top of all that the output images from all the render layers don’t have to be all packed into one gigantic EXR file,
You can use compositing operations and compositing ‘File Output’ node to determine exactly how the images will be stored in folders and files.
The ‘File Output’ node will actually create folders and store the files in them so output from one render command an be automatically stored within multiple folders.
In short.. AWESOME!!
Critical reminder: When setting up render layers make sure you don’t forget to turn them all on when your done testing, otherwise you’l come back to the studio in the morning and find that not all the needed sequences have been rendered :-\