In the SIK project #1, the diagram shows a wire from the 5v pin on the Arduino board to the breadboard + column. What is the purpose of this connection since it is not necessary to make the LED light up? The LED draws its power from pin 13 (or whatever pin 0-13 you choose to connect it to).
You're correct that it is not necessary. Perhaps it's to demonstrate the possibility of making that connection between the Arduino and the breadboard - and to get us in the habit of doing so?