When you root an Android device, you create a new “SuperUser” account on the device that gives you complete control over the operating system, like an Administrator account on your computer. Rooting is not illegal, but it may void your device’s warranty and some apps on a rooted phone can violate your carrier’s terms of service.
An Android device is a mobile computer, with a processor, internal memory and storage just like a desktop or laptop PC. The performance of your Android is based on the same factors that affect computer speed, such as available memory and processor speed. When you root your Android, you can install apps that let you remove memory-hogging programs included by your device’s manufacturer or mobile carrier, move the device’s data cache from internal memory to the microSD card and overclock the processor to make it run faster.
Unrooted Android devices support apps to backup contacts, SMS messages, the call log and apps. These apps are helpful if you get a new phone or accidentally delete something. For a full backup of everything on your Android device, including modifications to the operating system, you must use apps that require a rooted device. A full backup is also useful if you want to switch between and modified and stock version of the operating system or unroot your device.
Programming teams are regularly creating new full-system modifications for Android devices, called ROMs. ROMs are full-system image files that replace the stock operating system, and require a rooted Android. A ROM can add new functionality to your Android device like VPN, change the user interface and often includes the latest version of the Android operating system, even if your manufacturer or carrier has not released it for your device. With a rooted Android, you can sample the features of different ROMs to find the one that best meets your needs.