In an emotional froth of late I have found it difficult to sit in the studio and apply colors to canvas. But my artist mind requires exercising so I decided to develop new sketches for future paintings. Sketch books are a great place to work out perspective and compositional issues. Just because you "composed" it in the view finder of your Nikon D90 does not mean it will work well as a painting. Drawing allows you to erase! With my church paintings I often erase surrounding buildings or modifications to the basic structure that distract. I totally re-arrange canyon walls.
It is wise I think while sketching to not always look at a "finished" composition. The little detail sketches that populate the sketch books of Michelangelo and Da Vinci are a case in point. And often I have worked on a detail with the idea of where it would fit in a larger canvas to find it stands alone or that it dictates its own setting.
Sketching is letting the muse free. Always wise to keep the eraser at a distance. Don't worry about getting the anatomy just right - let the composition flow. I know I should free sketch more often. But when I am rushed to produce for a show it is often too easy to pull out a previous sketch and use all or part of it again for a new work. But in the last couple of days I have developed eight new prospective compositions by just sketching. And oh, the peace it has brought.