For example, if you want an ominous feel to a cathedral, you need to know what light colors are more ominous than others, what direction of lighting (maybe bottom up, rather than from the top), what types of lights...many dim point lights? or single directional lights?, if light scattering through a medium like fog would look good, etc etc. And also keeping in mind functional aspects like, can the player still see items or things he needs to do, even with all of this specific lighting.

Another example might be that while lighting and materials might behave naturally, sometimes they still behave in undesireable ways. Suppose the angle of the sun reflected off of a reflective surface right into the player's face right while he was at a specific location where he needed to do something. If you can't move the surface, can you shift the light? Will that effect the scene much? Maybe now that you shifted the light, the rays of light that were going through a tree branch beautifully are not there any more.