The second part of the unit 3 tutorial explain the usefulness of final gathering. They are used to calculate on which areas get more light and which areas doesn't which can be helpful if you feel that a certain area is not getting enough light or shade.
Final Gather Points
The last part of the unit 3 tutorial is global illumination, which is adding the right amount of light in a room to give it and producing a ray of light out of a window or any hole.
All of the tutorials are very helpful in giving me ideas in rendering out scenes for my animation.