Most power users want to re-root their Android devices to take full control of the system. While Android devices are very strong, the average user unfortunately, locked out of some features. They can not tamper with system files or choose to remove elements of the pre-installed them and they may not like.
Rooting is the solution to these problems; on a device that has been at the root, you can do away with the bloat-ware (application pre-installed by the manufacturer and operator) which can slow down the device or consuming unnecessary memory, bandwidth and battery. However, rooting cause you to lose the warranty you. If you want to claim warranty you, you will need to unroot the device you before sending it back.