The more tools you can add to your "painting toolbox" the more you have to draw from to really say what you want in the way that you want. This exercise is another approach to applying paint and creating a variety in surface quality. In this exercise, I paint from a still life set up and handle the paint in a little more of a traditional approach, by keeping my darks thin and my lights thick. It's just another way to apply paint and adds variety to the surface. It's your job to find your own "voice" and there are many tools available and here's another one! Mileage, Mileage, Mileage.