I don't know why this thread went unnoticed. Here is my non-scientific explanation:
We could theoretically have a totally unbiased renderer, but it would be really slow, because many effects would take a lot of computing power with just little or no benefit.
That is why in most renderers, including Corona, we have some "bias" such as: limited number of light bounces, reflections, and refractions; maximum sample intensity, autobump instead of displacement, etc.
In Corona, the default render settings are optimal for most scenes.
If you are rendering an interior animation, I would mostly focus of setting up the UHD Cache correctly:
https://coronarenderer.freshdesk.com/support/solutions/articles/5000515648
