Why Grid is important in the model:
Grid is the basic element in the model based on the grid we shall locate the element position in the model.
Once we create the grid in model (3d view we can extract 2d view each grid line) we can extract 2d view of grid in form of Elevation and plans. Based on that view we can easily locate or place the element in the model.
You can place grid in any form (Rectangular / Inclined /Circular)