Spaces can be used at the early stages of the project to create the concept. You can use them to show areas and volumes, allowing you to create the plans quickly, as well as beating able to show the client a quick 3D model. Many clients struggle to visualise the plan in 3D, so the spaces are really useful for showing the 3D form. If you have the 3D form, you can create solar studies, or you could use the spaces as a wireframe and sketch over them. An important part of the spaces is that they remain valuable right through the design and documentation process for calculating areas, budgets, occupancy, room finishes, etc.