PS-ing for special effects or supplemental lighting) is when you say to yourself, "Gee, it sure is a crappy day outside." You want total overcast so that basically you can't see any shadows on the ground. Then the color saturation of your subject will be at a max, and the light will be diffuse. If the sun is out, then the earliest or latest in the day is best. You want to have your point source to be from the side, rather than light from overhead. Sunsets and sunrises are good for that reason independent of the landscape itself. Using side lighting is even more important when shooting faces of peeps. But I'm sure you have heard all this before. There are exceptions to every rule but those are some of the general principles.
