Hashgachot

Question

From your replies I have learnt that you don't need a hashgacha on an ice cream store if you find out what the ingredients are. I think you even said that nothing is gained by such a hashgacha. But the Lakewood Kashrut Organization does put hashgachot on some Carvels and TCBYs, implying that while perhaps not necessary, the hashgacha provides some added kashrut protection. Please clarify. Thanks