A roadmap is a forecast of a possible future, it is not fixed. You are visualizing the possible future.
While a roadmap is important to communicate to the board, it adds the most value to a team. A frequently forecasted roadmap enables a team to build better products.
Roadmaps also contribute to keeping up morale. Going on a journey with your team is compelling and exciting as compared to not having any direction. Knowing where you are going matters.
The receivers of the forecast (customers) must know that the dynamics of it are going to change, and that responsibility is on you. The updates must not be thrown out there and left open to interpretation - they need to be explained.
Professional accountability is key with forecasting; all members of the team must also be continually updated with all new information.
If you made a promise to a client early on, you cannot expect the rest of your team to pick up the slack if the forecast was incorrect. It is vital to update the roadmap and all members involved as things move along.
Cone of uncertainty: do not make promises to your customers during inception and elaboration of a project. As you’ve had time to firm things up, you can paint a clearer picture at the construction stage.
Good quality roadmaps will continually add value to a project.