Document existing conditions before a project or as-builts afterwards. Pre-contruction documentation is critical for the design phase of any renovations and especially for historic buildings where the walls and floors that are sloped and non-uniform.
Documenting existing conditions is also helpful when determining how much a roof has sagged or a foundation has sunk. When owning an older building it is good insurance to document these conditions at the beginning of your ownership to prove that there has been no further settlement by the time you want to sell.
Documenting the maze of wiring and pipes in a space before concealing it behind sheet rock can save future headaches.
How will this new house look in its neighborhood? 3D scanning and photogrammetry can also create visualizations of the street where you plan to build a house. The resulting point cloud can be combined with CAD software like Revit or SketchUp to put the architectural plan into 3D context in its surroundings.