Backgrounds appear behind the functional elements of your app. 
Consider this an opportunity to display branding or other custom art to set the tone for your app. 
Backgrounds can also be dynamic, presenting new or changing information or images at specific intervals. 
Panoramas, for example, can contain a background image that spans all of its panels. 
An app Tile can have its background image updated at any time using the Microsoft Push Notification Service or a Tile Schedule.