When a painter works on a canvas one element leads to the next. There is a constant process of assessment, inclusion, and elimination. The nature of the work is always before the painter as the work cummulatively evolves. Film animators were forced to work blind. Their medium was motion imaging, but they wouldn't see the motion until the film was developed and printed.
Digital animators fare slightly better.
3D people can view wireframe previews of their work, but they still must wait long periods for animated segments to render before they can relate to the true nature of what they are doing. Electronic motion imaging that responds and displays immediately is universally the ideal. Choices are made, as they are in music, from moment to moment as the need arises. Great music composition is an act of improvisation. Both Mozart and Chopin improvised their pieces first and then transcribed them.