It has been said that there is a loophole in the Samsung Galaxy S5 that allows the user to unlock the device easily and quickly.
In some Samsung Galaxy S5 handsets that are bootloader locked with the Qualcomm processor, the bootloader may be unlocked. This means that the owner is able to unlock the bootloader of the handset and then install a custom ROM of their choice.
Apparently owners are able to run it and this changes some bytes in the eMMC, they can then go ahead and unlock the bootloader on the PC.
Providing that you do it correctly the risk to the Samsung Galaxy S5 is only the same as when flashing a bootloader or when going into recovery.