Hi there. I'm wondering if PBR is physically correct then it should be obvious to keep a correct object scale. So for example if my model of a bottle is 1x1x1 then it's really huge bottle and PBR do all it's calculations incorrectly and theoretically longer.
Let me know your thoughts guys.

PBR speed is not dependent on scale of your scene so it doesn't really matter for that

there are however some properties dependent on the scene scale (in camera space) like ray bias, displacements, attenuations in your materials, lights, …, so it makes sense to tweak them for your scene scale
but always make sure your camera is not scaled (at least not without purpose)

I also agree with Tamte, Camera is scale is a NO NO. We were scaling maya cameras 100 times smaller, it made all the Volumes render super dense, created crazy amount of noise, etc.

Light works the same at all scales for rendering. Physically Based Rendering is essentially maths equations concerning energy conservation and the way light bounces off surfaces.

http://www.pbrt.org [pbrt.org]

the only recomendation is keep the same scale scene all the time.
some shaders are affected by ray distance, that might affect things,
also the Bias in mantra you might have to raise it from .001 to .01.

if you can make sure you work in meters that way all the units wont have crazy values .

thanks. So answer is yes. It doesn't take additional render time but it's always good to keep real world object scale