Render Passes or Render Layers are an extremely valuable tool in the rendering of 3D CGI elements. Render Layers allow the user to perform rendering tasks in the most efficient from possible allowing a lot of flexibility in the compositing stages.
A Render Layer basically allows the user to render different elements of a 3D scene separately, such as shadows, light sources and ambient occlusion as well as much more. Rendering all of these elements at once can be very taxing on the computers ability to perform. Having all of these details on one layer also allows for very little flexibility in the later composition stages.
If all the details are rendered separately as they are using Render Layers it means that they can be individually edited in the post production stage. For example elements such as particular light sources can be altered in many ways without requiring to be re-rendered. A composition that has not utilized these render layers will not be able to achieve this kind of control of individual elements. Instead only the scene as a whole can be edited, re-rendering required for additional control.
Martin, A.M. (13th Nov, 2015.) 15T3 ANI210 WEEK 8 RESEARCH. Retrieved from https://andrewmartinsae.wordpress.com/
Shaheen, M.S. (28th Aug.) What is a Render Pass or Render Layer, and why is it often necessary to render 3D CG elements in parts and put them together in compositing? Retrieved from http://mshaheenstudio1.blogspot.com.au/2015/08/what-is-render-pass-or-render-layer-and.html?view=flipcard&m=1
wiplow [Image] (8th April.) Retrieved from https://adekunleadekayeroblog.wordpress.com/2015/04/08/render-layers-and-passes/
68324-hercules_passes [Image] (8th Dec, 2014.) Retrieved from https://3dwally.wordpress.com/
95f99-hercules_render2 [Image] (8th Dec,2014.) Retrieved from https://3dwally.wordpress.com/