You need to submit drawings(site map, floor plan, elevations, construction details) for construction approval from the powers that be...
And these days, the powers that be, require digital submission of all documentation...
With a 3D model, You get to see what your project will look like before begining, or contracting for, a construction project...
With a 3D model and Drawings you can estimate material costs yourself, before hiring a contractor...
With a 3D model and Drawings in hand, you can have serious, detailed, conversations with potential contractors regarding what you expect the finished project to look like when it's complete. No misunderstandings or doubts about the expected outcome...
Once the 3D model is created any changes or additional work/details can be input and the 3D model revised easily...
With a 3D model and drawings in hand, you are in control of the project and not at the mercy of a contractors imagination...