Originally designed to enhance the painting experience by mixing pixels as though they were watercolor paint, one of the brush tools I have found a photographic use for is the Mixer Brush tool. Using the Wet, Load and Mix controls, along with the Load brush and Clean brush options, you can reload your brush with “paint” after each brush stroke, clean the brush and control the amount of water on the brush.
Like the new brush tips, many photographers and videographers may wonder how the Mixer brush can help their workflow. I’ve found the Mixer Brush to be a nice addition to my burning and dodging workflow. It gives a softer, cleaner effect than the standard brushes, though it requires a slightly different approach.
Typically, I create a new layer, set the layer blending mode to Overlay and fill the layer with 50% gray. Painting with either black or white using a soft brush set to 10% brush opacity burns or dodges the image respectively. With the Mixing Brush tool, I use the same layer setup, but change the layer opacity to 10% and set the Mixing Brush preset to Moist, Light Mix. Painting with a soft brush set to either black (burn) or white (dodge) provides a subtle, soft effect without the visible brush strokes or uneven tonal changes that can appear when using the previous method.
So, if you routinely burn and dodge your photos (or video in PS Extended), give the Mixer Brush tool a try to see if it suits your needs.