For example, If you had an found a really good OP sword at and end city, or just enchanted something really expensive, but it has Bane of arthropods on it, The grindstone will allow you to pick out which enchantment you want to remove, (hence the bane of arthropods enchantment)
Sure, it would be a bit OP, but i think this would be SO useful.
Caption this Meme
