This method downgrades your anti-rollback version. Do this incorrectly, and you hard-brick the phone.
This official path was a lie for 90% of users. LG, bowing to carrier demands (AT&T, Verizon, T-Mobile USA, Sprint, etc.), hard-locked the bootloaders on all (H810, H811, VS986, LS991). The official unlock worked only for: lg g4 unlock bootloader