Flea dips offer some residual protection. They repel fleas for a certain amount of time after you dip your cat. However, since a flea dip remains on a cat's fur, the cat will ingest it when it grooms itself. Therefore, some veterinarians don't recommend flea-dipping for cats. Flea collars kill fleas on the cat's face and neck, but they don't kill all of the fleas on a cat's body.
Some cats are allergic to flea collars and develop a rash or lose the fur on their necks.
In addition, most flea collar aren't breakaway, which means they aren't elastic and they won't slip off if your cat gets tangled. Most veterinarians discourage flea medallions because they can dangle into a cat's water and contaminate it. Flea sprays and powders are available too, some of which are very good. Just make sure the product is designed for your cat and not for your house. Never treat your cat with more than one product at a time, and it's a good idea to ask your veterinarian to recommend flea products for your cat.