Bootloader is the heart of Android Rooting because bootloader allows you to install Custom ROMs in your Android device. As Custom ROM is not as the same as original OS (Stock ROM). And Custom ROM can cause your phone and already installed apps to stop working exactly how it should work.
Things you should remember while unlocking bootloader
Let me tell you that on unlocking the bootloader will void your phone’s warranty. Weather it’s an Official Firmware or Unofficial Firmware on unlocking the bootloader on your device, the phone manufacturer will not be able take any guarantee of your device to work properly.
The methods can be different for unlocking bootloader on Android smartphones depending on device manufacturer.