There are oils on a cat's fur to make it soft and shiny. If you wash a cat too often,its fur will get too dry.
Also washing a cat when the weather is cold,may cause colds' eye infections or ear infections. Also some cats are allergic to the shampoo or soap that you use in thir bath.
So before giving your cat a bath
So before giving your cat a bath,you should wash a small part of its fur with shampoo to check if there's any skin reaction.