Rooting an Android phone gives the user control over the device's root system, giving a user more control over how it works. With a rooted phone, the user is able to install apps that the unit normally does not allow. The process has the potential to increase performance.
The benefits of rooting are not all positive. Rooting eliminates some of the protection the manufacturer builds into the unit. Without this protection, it is possible to corrupt the operating system so the phone is no longer usable. Rooting also voids the manufacturer's warranty. Less severe consequences include an increased chance of a virus affecting the cellphone and decreased overall performance.