This is primarily useful for pack makers. There are quite a few mods that render normally passive mobs hostile, or force neutral mobs into hostility (notably iron golems). These mobs cannot be calmed with their respective charms (should the pack create ways to acquire them) because the charm aggro check reads off the charm registry list, which is only generated for hostile mobs. I'm not sure what the best way to navigate around this would be, but it'd be nice to have them extend to all MobEntitys. I'd imagine modifying the registry to accept all mobs, then restricting the drops to hostile mobs in the drop event would maintain the current effects?