This will allow more granular manipulation of loot for a mob over and beyond it's general type. For my particular use case I am wanting to add an NBT tag "BySpawner" using spawn.json if a mob was spawned by a spawner, and then cause all drops to be removed from said mob by a loot rule in loot.json that would match based on the NBT.

I could imagine there would be other uses as well. For example, a Zombie boss that is tougher than a normal zombie could be tagged with "SuperZombie". When apply loot drops a loot rule would match on "SuperZombie".

(I would think experience.json could benefit from these things as well.)