The main advantage is it gives me expanded preparation time. After I draw the scene onto my canvas I then begin to slowly tint the canvas with pigment. I use a lot of mineral spirits at this point. The paint dries quickly so I can correct color and value during the next painting session by loosely painting over the areas needing correction. All I worry about is hue and value. If I make mistakes and paint a distant mesa too dark I can scumble a lighter, bluer color over the top and slowly refine the color and value. As I do this I find that the quality of the paint surface becomes busy and blotchy, especially from close up. From a distance this painting technique can look quite nice. When the painting looks good from a distance you know that your underpainting is done and you can proceed to the next phase.
I now let the thin underpainting dry completely. I then oil up the canvas using a variety of oils or putties (in the case of the desert scene I used Venetian medium from Natural Pigments). I then mix up a series of pigments and closely match the values to the canvas surface. I ensure correct values by holding up the brush with a bit of paint on the tip. In this way I can match value and hue with extreme accuracy. I mix up rich, thick, strokes of broken color and apply this color using the methods described in earlier videos. The thickness of the Venetian medium allows me to apply thicker paint. I like a medium that has a lot of body that pulls the paint off my brush.
For those who wonder if this technique is worth the effort I can only say that with some subjects this method will ensure success when others fail. I find that as long as I don’t get impatient the process is extremely enjoyable. This method helps ensure accurate color and value and provides a safety net in the challenging and often exasperating world of thick paint.