Required and usedEdit
Here you declare what hardware or software features are used by the application. The purpose of a uses-feature declaration is to inform any external entity of the set of hardware and software features on which your application depends. The element offers a required attribute that lets you specify whether your application requires and cannot function without the declared feature, or whether it prefers to have the feature but can function without it.
Because feature support can vary across Android devices, the uses-feature element serves an important role in letting an application describe the device-variable features that it uses