This allows you to choose your notification sound to help you identify exactly what notification you are receiving.
Each type of notification can have a different sound to help you identify its severity.
To change sounds you will need to click on the little cog located at the top right of the screen. (see screenshot)
Then a menu will pop up. Click preferences.
Choosing your notification
Here you can choose a notification to have its own sound.
This was added so that the user understood exactly what notification is being received by the sound.
Here is the list of sounds you can choose from for each notification.
This can be accessed by clicking on one of the blue buttons.