Sometimes ideas for composition just come to you, fully formed. Other times you have to build them from scratch. In both cases, you still need to play with the idea to develop it. Once you start to render, there many other things to work out that you may not notice serious compositional flaws. Once you have committed a lot of effort to developing a view, you may be reluctant to make changes.
If ten people set up to render the same thing you'll get ten different renders People see from different points of view, both literally and figuratively. Everyone has cliched ways of looking at things. Breaking those habits and taking a fresh viewpoint is vital to the artistic process. You know the experience of seeing something familiar as if for the first time; it seems alive and exciting. That's the way you want to try to see things before you render.