Coordinate systems and grid lines provide a locating scheme by representing the relative positioning requirements for a specific design purpose. When designing your model, you might want different coordinate systems for individual pipe racks, buildings, or areas of the model.
When designing your ship, you might want to create a main coordinate system with grid and Z planes every meter. The software uses the grid planes and Z planes of this coordinate system to place the major plate systems of the ship, such as the decks and bulkheads. You might also want to create separate coordinates systems for individual cargo spaces and machinery spaces to help with equipment placement.