Ok, I've made some tests. The results are pretty obvious but maybe someone will find this useful. It illustrates how important it is to keep realistic physical scale (is this the right term here?) for optimal quality/render time.
I set material's diffuse colour to 255 white and then changed diffuse level like this: 0,5 0,25 0,125 0,0625 so basically I cut it in half. There was also one render (0.jpg) where diffuse level was set to 0,9.
I also changed light intensity and most important: gamma to make the images as similar as possible. I know they will never be identical but this proves how fast you can render something and then do some adjustments to make it look almost the same as something that took much much longer to render.
Check out the render times. Imagine rendering something more complex with such render time differences and almost no quality difference.
If I'm writing some utter bullshit here, then correct me please.
