A recent report suggests that Sony Mobile is refusing to repair hardware issues on devices which have an unlocked bootloader. So anyone who is planning to purchase a Sony device and unlock the bootloader should be aware of this.
Sony has issued a statement on their website which warns users that the warranty may be voided if the device is unlocked.
"Please note that you may void the warranty of your phone and/or any warranty from your operator if you unlock the boot loader."What's strange however is that the unlocking tool in fact is an official tool provided by Sony itself. What’s worse is that Sony is even using this as an excuse to avoid repairing the yellow tint hardware issues on certain devices.
So keep in mind that while Sony themselves are providing tools to unlock your devices, using it to unlock your device is deemed ‘illegal’. You may want to check and ensure your Sony device is fully free of any manufacturer defects before you decide to enjoy the freedom Android usually offers.
source - XperiaBlog