Just finished teaching a plein air workshop, and wow there is no faster way to accelerate your growth , as plein air quickly forces you to make decisions, but really the most important thing about it is you just cannot get the color harmonies from a picture, and dark and light values are too blown out.
Once you get the shape design right , really observing the harmonies and taking the time to mix the colors correctly is just amazingly enjoyable and rewarding, just paying attention to the subtle lighting effects. I have tried to capture this inside and the effects are not even close. Just another great reason to enjoy nature. They may not all be a success but they are all a learning experience.