An ah-ha moment!
Notice how the paint in the mixing area is very close to the paint that has dried on the paper on the left? The “value” of each is the same.
And, notice how easy it is to see the color too? Because the paint has been “thinned” by placing the entire palette at an angle (15 degrees) the paint spreads nicely downward, revealing what the paint will look like on the painting. I got this from an artist that paints YouTube paintings. And while they do not mention it in their videos, I think they do this for the same reasons. Do you agree?