It makes sense to take a good look at a new image or scene with an eye toward what is likely to interrupt the flow of translating the subject into watercolor. It's wonderful to allow the painting process to unfold steadily, with some room reserved for inspiration. Coming to an unresolved passage of the scene can bring the painter to a complete stop, and interject tension that undermines the pleasure of bringing brush to paper.
Identifying the tricky parts in advance offers an opportunity to practice the technique and approach you think might work. It is often not necessary to paint a full version of the subject to get answers to your questions. For example, The cliff and the water in this scene are in extreme contrast to each other. If you simply want to know how it would look for the contrast to be lessened, you could adjust the value of the adjacent shapes on a few scraps of paper.