It basically adds more sounds to lib SharedMedia so it can be used with AddOns like WeakAuras.
The offered sound mostly focus on the raiding / dungeon scene.
The added sounds are marked in red, as seen here:

How to make sounds louder:

1. Simply go to System -> Sound (ingame)
2. Increase "Master Volume" slider to max (recommended)
3. Decrease slider of other sounds channels (sound,music,ambience,dialog)