In August 2017, Oculus released the Oculus Stereo Shading Re-Projection Sample asset package to the Unity Asset Store. This package provided an innovative technique to optimize VR rendering. The technique uses a two-pass approach. In the first pass, rendered pixels from one eye are re-projected to the other eye. Then, in a second rendering pass, the gaps are filled in.

The Oculus Stereo Shading Re-Projection Sample asset package contains an instructional text file and all necessary content, such as materials, prefabs, shaders, scripts, textures, and a scene. 

Oculus VR reports that this re-projection approach saves over 20% GPU cost per frame. Your results might vary, but the sheer possibility of optimization on this scale makes checking this asset package out a must.