They should be trimmed at least once a month so they don't get ingrown nails. As cats get older and don't use things to scratch on they can get ingrown nails. usually a cat who can use a scratching post kind of takes care of this himself. However, to keep your cat from clinging to you, or scratching you, it's a good idea to trim them.REALLY???? I`ve never trimmed mine either! Why is it that they need to be trimmed??? Just curious!