This is a simple technique that helped me focus on my painting and coloring skills while having an realistic outline sketch of what I wanted to draw. I used this method for many years while at the same time practicing sketching.
I have noticed that many of my students to not enjoy sketching/drawing as much as they do coloring. This method helps them and can help you focus on what you enjoy most.
In some cases it is hard to accurately draw what you want to paint..but with the tracing transfer method you can be sure to get an accurate drawing every time no matter what!