By default, all the objects in Owlet scene belong to a single rendering layer. You can add more layers and assign objects to them. Then at rendering time you can render each layer to a separate image, separating your scene on a per-object basis. This way you can make more complex post-processing, compared to the single-image output.
You can toggle the rendering layers panel using the View menu:
Use the PLUS and MINUS buttons at the bottom to add and remove layers, use Rename button to change the selected layer’s name. Once the list is ready, you can assign nodes to layers in the node properties panel:
Once this done you can enable layers rendering in rendering settings window:
Then after rendering you get either multiple output files (one per layer), or a multilayered PSD file if you save to PSD format.