Can you bathe a cat in dish soap?
You shouldn't, because it is too harsh for their skin. You should use cat shampoo, or if you don't have any cat shampoo, you can use baby shampoo, but not dish soap nor regular human shampoo for adults.
It is not essential to bathe your cat, but many owners do like to bathe their cats. Bathing can be needed if the cat develops a skin problem or other skin or fur based issue, but as for cleanliness a healthy cat will clean itself often and thoroughly. It is entirely your personal preference if you wish to bathe your cat or not.