Figure 10 demonstrates how I might use the Gouache Blair Brush for foliage in addition to hair shown in Figure 9. Flowers and other plants have leaves and petals that can be simplified into 2-3 planes. They are made of simple shapes, but assembled together it can be quite detailed and overwhelming. Painting them in a planar method makes it possible to paint a field of flowers realistically without your hand falling off.
Mixer Brushes
Mixer Brushes are popular for digital painters and can be used in the same way as Smudge Brushes for solid pixels. The brush dynamics are different from Smudge Brushes and may take some fiddling with. I find the best use for Mixer brushes to be smooth, oily, and painterly styles. I don't use Mixer Brushes as much because the Smudge Brushes tackle both pixels on transparent areas as well as solid pixels. I also have been moving away from using the mixer brush for technique reasons since I want to keep my grainy under-layer visible as much as possible.