Make niche diets more accessible
Providing what kinds of meat/fish are used in a non-vegetarian product could help make informed choices for more niche diets, like pescetarian or maybe religious based.
Manufacturers don't always make it clear what kinds of animals are used in their products (i.e. gelatine). Displaying that it can potentially contain pork could help for Jewish, Islamic, and some Christian orthodox diets, while warning that it could potentially contain beef could help for Hindu diets. Same goes for pescetarian diets, to show that the product is not vegetarian, because it contains fish, but no meat present.
Providing other potentially contained meats, could also help users to exclude some products.
Also there is a difference between lacto-ovo-vegetarian diet (includes eggs), and purely lacto-vegetarian (excludes eggs), which is the common one in some Asian countries where the eggs are not considered vegetarian. Currently it is possible to select vegetarian diet and eggs as an allergen to exclude them, but it's not clear, and many users might not know this, thus getting wrong filters by accident.