On-screen navigation bar is waste of display space on Android applications that do not support full screen immersive mode. Luckily, Google created that mode for Nexus devices without hardware navigation keys. But not all applications and games support full screen immersive mode yet. So you are not getting the full display out of it. Thanks to GMD Full Screen Immersive Mode, we can enjoy full screen mode on all Android applications and games even they do not support it. And no root access is required. A nice to have on Nexus devices like Nexus 7 (2013) and Nexus 5.
Note – you need KitKat or higher Android version that supports immersive mode in order to use this application. And there are some known issues too. Get more information here.