So, you are supposed to normalize a BRDF equation so that it sums to 1 over the hemisphere. It seems that everybody goes out of their way to normalize the NDF portion; however, I was wondering about the other portions. Wouldn't it make sense to normalize the whole equation including the Fresnel term for example? I did some Google searching and came across this:

http://seblagarde.wordpress.com/2011/08/17/hello-world/

"When working with microfacet BRDFs, normalize only microfacet normal distribution function (NDF)"

…but then I ask myself, why? The writer doesn’t seem to give any explanation why. Does anybody know?