A Revit project has internal coordinates for all the elements that compose the model in a project. Those coordinates are known to this project only. This is acceptable if you have a standalone model whose position is not relevant to other models or to a site. However, if you want the position of the model to be known to other linked models, you need to share coordinates.
Video: Shared Positioning
If the significant coordinates for a project are in a linked model, such as a building model with a linked site, acquire the coordinates from the linked model.
If the significant coordinates for a project are in the host model, such as a site with linked building models, publish coordinates from the host to the linked models.