Inverse Square Law of Lighting

What is the inverse square law of light? How does this affect you when you are lighting a scene?  What do you need to keep in mind?

    The inverse square law of light is used to calculate the fall-off of a light source as you increase/decrease the distance from the subject. Regarding light fall-off, a light source emits a set number of rays on the subject. When it's closer, the rays are more condensed and make the light appear brighter and stronger. When the light source is further, it spreads those rays across more space, creating a sort of feathered look and decreasing the amount of light that is actually hitting the subject. The exact formula for the inverse square law of light when increasing the distance is i=1/d^(2), with "i" being intensity and "d" being distance. What this formula tells you is how much the intensity decreases based on the distance. For instance, when you increase the distance of a light from the subject by 2 times, the intensity is 1/4 the amount of light. When you want to move the light closer, the formula is i=d^(2). This affects me when I'm lighting a scene because I may need to adjust my lighting either to get a more desired look or to fix issues such as unwanted lights overpowering the lights that I do want. The main thing that I need to keep in mind is that the closer a light, the more intense, and the further the light, the less intense.