Is it really necessary to bathe your cat? In a nutshell, no. After all, cats are excellent at grooming themselves. They spend much of their time cleaning themselves.
They are usually very capable of keeping their coats clean on their own. Despite your cat's feelings, there are some situations where shampoo and water are required. Since a Persian cat has long hair, it may require more grooming than she can handle. Hairless cats such as Sphinx, need bathing on a regular basis to eliminate body oils that are usually absorbed by the hair they lack.
Your cat may also require a bath for medical reasons. Cats who are elderly, obese, or have mobility problems may find it difficult to keep themselves clean (at least to cat standards). Giving your cat a weekly washing can effectively reduce illness cat dander especially if you have a human family member with a cat allergy.
A bath can be helpful to your cat's skin and coat if done properly. Just keep in mind that this does not guarantee that it will like it.