The reintroduced Unlock bootloader service requires only three main steps to unlock an Xperia device’s boot loader. Just select your device and enter an email address, submit your IMEI number and get your unlock code, then perform the actual unlocking of the device. Why unlocking the bootloader? By unlocking the bootloader anyone with proper skills can modify and enhance their Android phone. To install custom recovery, custom ROM or apps that require root access, you should first unlock the bootloader (source)
