The downside? You lose official OTA (Over-the-Air) update convenience. While you can still update manually, you cannot accept an automatic OTA on an unlocked device without risking a bootloop.
Unlocking the bootloader disables this signature check. This allows you to flash custom images, but it also means your phone will no longer verify the integrity of the OS at startup. asus zenfone 9 unlock bootloader
You rely on Netflix in HD, you have no PC to fix boot loops, or your model is a carrier-locked variant. The downside