The Render Diagnostics tool lets you monitor how well you optimize the scene for rendering and watch for limitations and potential problems that may occur. For example, surfaces that are far away or blurred may not require the same level of visual accuracy or photo realism as surfaces close to the camera. You can speed render times and reduce memory usage if you know what the renderer is doing.
Run Render Diagnostics after you adjust objects and before you render to obtain valuable information about how you can improve performance and avoid limitations. You can run the diagnostics while experimenting with rendering settings, or before you start the final rendering.
Hardware render diagnostics traverse the shading network and geometry to flag those features which are not supported in the same way as they are in software rendering. Render diagnostics also examines your graphics hardware to determine its level of support.
