When it comes to visual design, no amount of planning, discussing, estimating, describing, segmenting, tracking, assuming, or conceptualizing can replace seeing. It doesn't matter what is viewed - it could be a rough doodle on a napkin - but that first glimpse of something tangible will anchor all future visual development.
Much like in a negotiation, the first real image is like the the first offer. It is the launch pad for future discussion and redirectioning. The earlier that first visual is shared, the earlier that a real negotiation can begin.