Waffles HATES water like most cats do so she only gets showered if she gets mucky for some reason and I don't see it as reasonable for her to clean off (ie litter tray mess).
When I have washed her she wails, meows and scratches like mad and I can feel her heart pounding as I have to restrain her to do it. So, I personally wouldn't do it unless it was necessary.
The other day some fur on the back of her head was a little hard (something matted there) and the next day it was completely smooth and clean again so they can manage on their own.
IMO unless a cat likes it or it is necessary I find it a little cruel to wash cats.