Hi Brian,

yesterday i`ve made some tests again and i couldn`t detect much difference by using fresnel or not.
I am a bit biased by the unbiased renderengines like Maxwell and Fryrender(nice worldplay :-)) and they have turned fresnel all the time on , cause you can`t turn it off. You just change it`s intesity mainly by the ior and by roughness.
I`ve here one tutorial which is about procedural textures in c4d and there the author uses fresnel. Inside the tutorial he has two images, one with fresnel turned on and one without it, so you can compare its effect.
Unfortunenatly the tutorial is in spanish. I can`t speak or read spanish either but the images are named in english so you can easily see of what i spoke here. The link to the english text seems to be broken, so here is the spanish one:

http://www.3dluvr.com/carles/Tut02es.htm

The fresnel effect in a way accents three- dimensionality when there are reflections visible on an object.


Greetings
Dirk