Foundation: Beyond first written drafts and outlines of a project, concept art gives a visual baseline for everything that follows. It sets a tone and style that strongly informs the rest of the design work.
Alignment: Concept art is an excellent tool for ensuring everyone shares a similar vision of where a project is heading early on in the process. Words often fail to capture what a picture communicates effortlessly, so creating and agreeing on concept art can be a revealing process and save a lot of confusion later down the line.
Impact: When growing a project and trying to get partners or consumers excited about it, a beautifully crafted image is much more powerful than a few paragraphs of text. Adding concept art to a project makes it more tangible, exciting, and engaging for everyone involved.