Render Layer
For example, we will render characters and backgrounds in separate layers.
In this case,
Character layer:
there will be reflections from the ground and walls upon the surface of the character.
If there is a wall between the character and the light source, a shadow will fall upon the character.
Backgroud layer:
The shadow of the character will fall upon the ground and walls of the background, and in areas that cast reflection, such as glass, you will see reflections of the character.
In this link, you will see divided into individual layers, the foreground airplane and its propellers, the background airplane firing its bullets, and the background.
Render Pass
This function creates output through the extraction of several elements, such as reflection and refraction.
http://core-cg.com/documentation/refpasses.html
We are considering the use of a game engine solution for rendering cinematic VFX(visual effects) and computer animation.
In order to combine with our standard workflows, ultimately it will be necessary for the compositing staff to make fine-tuning adjustments using tools such as Nuke and After Effects.
Therefore, we would like the game engine to output layer and pass separately.