Imagine you just bought a reading lamp for your home office. Instead of simply plugging it into a wall outlet, your only option is to run a power cord all the way down to the basement to connect it to the fuse box. If you decide to move the light into one of the bedrooms, you have to move it AND re-route the long power cord as well. Worse yet, if you want to use a different lamp from a different manufacturer, you need to run a different power cord down to the basement. Sounds annoying, right?
