The point is during a battle of like 30vs1 (for example few jedi & tons of troopers vs Grievous), there's no way gm can 100% control the lore charactor (Grievous) wont die during the mess boss fight, as a gm, we need to make sure that the lore charactor wont die, but meanwhile we want players enjoy the boss fight, it's a high pressure for gm which making us dont want to take the risk to make lore charactor event
Also we have rules for /sethealth for lore charactor, we cant set them like 100,000,000 health, that would just making players thinking they wont able to kill grievous, the purpose of this command is we dont want the lore charactor die and we want players think the grievous is killable and enjoy their fight (which their hp will shows on the bossbar)