Blender's Noise Threshold setting

Richard van der Oost is working on a series of articles on how render settings in Blender affect render time and quality.

In this article I cover the noise threshold setting in Blender, in the context of render optimization. (rendering faster and/or cheaper)

I will show a practical example of a scene where it can solve a common problem. And I will also dive into more of the math behind it. For example: how the noise that Blender measures relates to render time.