I clean my kitchen as I go also, but I use one bowl to mix my buttercream and another to mix my fillings, which normally I use at about the same time. Otherwise, I would be mixing buttercream, transferring to another bowl, washing the bowl, mixing filling, doing my cakes, washing two bowls. . .without my extra bowl I would have more steps and more dirty dishes. I'm all about economy of energy - I have lots to do.