Re: There's only one sun.

Very true, if your scene is outdoors in bright daylignt. You only have to worry about a single infinite light source if you're omitting fill light in the sake of realism. But at night there are street lights, lights flooding out through windows, etc. And then there's indoors at any time of day: light coming from multiple sources, all casting shadows, as well as the daylight coming through the window. That's when we need to worry about the complexities of having several light sources. It's not realistic in an office scene, for example, to have a single infinite light source. But hey, I'm all for doing everything outside under a blue sky. :)