It makes your youtube video volume output at it's maximum as long as you have 100% on.
As of
This script overwrites the default volume set (0.48) to 1. It's not the same as making your Video at 100% in your graphical interface, it makes the video even louder. (In most cases, if the video isn't at its maximum output in sound)
As long as the Video is at 100% in the user interface of youtube, the default volume value with be changed to 1 for the video, giving you the maximux output of sound this video can deliver you.
