Three-Way switches are used anytime a person wants to control a light from two different locations. For example a hallway may have a switch at both ends for controlling the hall light.
But when a person wants to control a light from more than two locations then four-ways are needed. These tutorials are more into explaining how the switches work rather than how to wire them. There are many other tutorials already existing on wiring them. This video was created with the hope that after watching this one, the other tutorials will be easier to comprehend and a person will have a better chance in troubleshooting their circuits.