Cat scratches and bites can be bad. My dad was bitten by one of our cats years ago and had to be on antibiotics. I remember his hand and arm swelling quite badly.
I always wash and treat anyplace that a cat has scratched me. I have found that a scratch will swell and itch badly if I don't take care of it right away. I have never gotten a severe bite, but it's definitely a good idea to cleanse them!