Diving into the world of your vision and dissecting it, essentially gives it more substance as it would show you really understand the makeup of your image. Normally you would do this process before you start on an image or piece of art, most professionals do ..unless you have had years of practice (its part of the production pipeline I believe as well). But it is possible to do this when you have half an image/idea completed! as shown below.
Benefits of exacting things, allows to change the makeup of your image, stage it differently perhaps. Never know what the future may hold lets say you'd like to construct your concept into 3D for example plans are there ready to go.
These are only some of my rough samples below I started with years ago, have so much more to show! All accompanying reference images are from google.