The importance of energy-conserving materials
Fortunately for us (given all of these complex processes taking place), the one thing that we don't have to worry about when using either the Standard or V-Ray Materials is the need to balance out the various reflectance, transmittance, and reflectivity properties as both of these materials handle incoming and outgoing light energy in a physically accurate manner, which means that they can correctly be referred to as energy-conserving materials.
In the bad old days of computer graphics, before render engines like V-Ray came along, materials relied on the good judgment of the artist in order to create a good looking balance between diffuse and specular components, which unfortunately (without a decent grounding in the physics of light) is not quite as easy to do as it may at first sound. This is why many renders produced in the 1990s suffered from what came to be referred to as the CG look.
Note
It does need to be said that unrealistic materials...
