One real-world anchor for all models. The number-one reason models "don't sit" on each other in coordination. Every Revit model has a Project Base Point (internal reference) and a Survey Point (anchor to the surveyor's coordinate system). Shared coordinates are the agreement of all disciplines on the same real-world anchor - so when the structural model is linked into the architectural one, they meet in the right place, at the right elevation, at the right rotation.

Setting them correctly on day one of the project saves weeks of pain.