I like the way my colours are never perfect or true. If I don’t wash it, then, say when I’m mixing a green, it has tiny bits of red undertone and all of these beautiful browns and blues on the edges. Also, because every colour has pretty much every other colour in it because it has gradually been mixed in, the entire palette is unified so colours never look bad beside eachother. 
I hope that makes sense. It just makes for unique colours that are so far from the colours in the tube of paint.