First things first :-
1. What is bootloader?
> Bootloader is a piece of code that runs before android loads up. Bootloaders usually contain several ways to boot the OS kernel and also contain commands for debugging and/or modifying the kernel environment.
2. Benefits of unlocking bootloader?
> You can flash custom kernels/ROMs.
> You can ALWAYS root your device. (compelling, eh?)
> You can flash alpha builds of newer firmware ( generally newer android version ) which is under testing and not meant for end consumers.
3. Disadvantages of unlocking bootloader? ( Doesn't matter if you have backed up your TA)
> You may void your warranty.
> You may loose some proprietary vendor software such as Bravia Engine, Download Music info etc. due to removal of DRM security keys.
> OTA updater may refuse to update your device and pop up a 'Device's software modified' message.
4. Can i unlock my bootloader?
> Go to dialer
> Type *#*#7378423#*#*
> Service info > Configuration
> Rooting status :
"Bootloader unlock allowed" - You can unlock your bootloader
"Bootloader unlock not allowed" - You cannot unlock your bootloader
5. What is TA?
> Take it simple, restoring the TA img of your device will revert your device to clean state as it was before unlocking bootloader. Thus, all of the aforementioned demerits will start working again.
6. Can I backup my TA?
> Yes, if you haven't unlocked your bootloader.
TA Backup using DevShaft's Tool (needs root access) :
1. Visit the thread and download backup tool from here ( Read everything carefully )
2. Run the tool with usb debugging on.
3. Your TA will be backed up. You can find zip in backup folder.
4. Unzip it and check for TA img file which should be roughly around 2048 KB.
5. There you have it.
Unlocking bootloader :
You can unlock bootloader in two ways:
1. Official way (Instructions included)
2. FlashTool ( Recommended )
1. Generate your unlock key by entering your IMEI. (To check your IMEI - *#06# )
2. After you have the key, use flashtool or cmd prompt to unlock. (easy?)
3. To verify, check rooting status :
"Bootloader unlock done" - Congrats, you've successfully unlocked your bootloader.
Relocking your bootloader :
This is where your backed up TA comes into play :
1, Run the DevShaft tool and choose restore TA.
2. You will need to enter your IMEI.
3. After everything is completed, check again for rooting status.
"Bootloader unlock allowed" - You have relocked your bootloader.
PS: You may run into bootloop or some other problems after unlocking bootloader. Simply flash stock FTF to fix.