I made a video about this issue as some friendly folks in Turbosquid pointed out to me the reason I had these low poly artifacts in cycles renders of my models.
It turned out that this effect is not only happening in Cycles but also in Renderman and other packages as well. This is what is known as “Terminator artifact”.
This has got to do with just how shadows are rendered in polygonal models and actually this is expected behavior. Programmers of Blender Cycles knew very well this would happen. It kind of sucks though and at the moment we don’t have a lot of alternatives except stick with Blender internal render, subdivide our models or use softer lights to reduce the jagged shadows.
This is where Eevee will be super useful. I can’t wait get my hands on it.. (and it will even support Filmic Blender which is awesome).
Here is more information about low poly artifacts in cycles:
and here is a more technical explanation of it:
I made video about this topic. Please check it in Youtube.