I don't have a cat, but from what I understand most cats can clean themselves and some are not great at it and need a little help. Then of course if you let your cat wander outside, I'm sure they get more dirty than a cat that stays inside all the time.
I have 4 cats. Most of the time they look after themselves. Every now and then the floof gets poo stuck in his fur or the fat one comes home covered in some weird oil or something and they need bathing, but it's maybe once or twice a year.