Fresnel and BRDF

[Guest]

Am I correct by saying that reflections are calculated using Fresnel because this is a good approximation and is fast, if you were to use BRDF it would be more accurate but too slow to render? Vray has a simplified control for BRDF, blinn phong ward. But this is by no means physically accurate.

I am trying to understand it all and I cant seem to find an up to date correct answer.