Paint that is applied this way tends to create broken flecks of color that create a texture over paint that has already been applied. Scumbled paint can also blend with previously applied wet paint and can create transitions in color and value that might also indicate form. The stippling that occurs with jabbing a somewhat splayed brush creates a fine but uncontrolled texture, adding indeterminacy on a very small scale. When scumbling is done with a lighter color over an already dry darker color, a cloudy/airy effect can be achieved. Often, scumbling accentuates the surface texture of the panel/canvas or the dry strokes that have already been applied, as the scumbled paint tends to adhere to the highest points of the surface.
Featured: The Shepherd's Song by Pierre Puvis de Chavannes.