The few quick tests I did shows a softening/degredation of contrasts/shadows on some objects.
That, especially, on objects which should not be reflective.
In Carrara, we have the Reflection channel as basic. The Fresnel plugins being a more "specialised refinement" in that area.
(Carrara is pretty good with it's shading tree variables)

Unbiased engines also have blurry reflections/refractions on ALL objects. This is how you find materials in reality. For materials such as glass/chrome, the sampling must be cranked up very high. For biased engines it will make your render time painfully long, but is more accurate...

jonah