|Through the Hills 8x10 oil on canvas panel|
Speed isn't necessary to produce good art, and it may not serve to produce works for the gallery, since until its mastered our work appears raw, unfinished, even clumsy. Still it teaches important lessons, and faster than any other means I know of. Like consciousness of "the big picture". You need to decide what the painting will emphasize and then everything else must be subordinated in the design. When working slowly, in the studio, it's easy to get sidetracked into developing various things within the scene that create competition for the big picture. It's the big picture concept that supplies impact, and not just technical virtuosity.
Paint handling is another skill that develops quickly as you go for speed. How thick, thin, transparent, slippery the paint is makes a difference in what you're able to accomplish. Only way to gain the skill is by lots of time painting, but going for speed forces the issue and shortens the learning curve. Values and color judgement have to be brought into hand, there usually isn't time to develop a careful underpainting step to build upon.
When speed begins to be mastered, the artist usually finds pleasure in the spontaneity of the painting act. It's like jamming on a musical instrument, and coming up with some surprisingly nice stuff. It also gives the brushwork a freshness, and directness that is often appealing. Like any worthwhile skill, it comes at a price, and progress can seem painfully slow, but it's worth the discipline if you want to play the music you see.