The international LG G4 is getting official TWRP starting today. People with a flair for modding must have heard of TWRP by now because this is the most popular custom recovery you can find. It is only available for the international version though, so keep that in mind. The phones sold by carriers, other than version H815, are still locked at the moment.
An unlocked boot loader means you will not be able to flash any software, including a custom recovery. TWRP support will make it possible for users to flash ROMs, make system backups and more. Be careful when you flash things on your device though, things can happen. Unlike other devices, LG makes reflashing stock software really really difficult.