This tutorial demonstrates several features that can help you manage large surfaces efficiently in AutoCAD Civil 3D.
Because surfaces can contain large amounts of data, it is important to use only as much data is necessary for the current task. For example, when building a surface from LIDAR data, the corresponding point file can contain millions of points. If all of those points are included in the surface definition, it can take a considerable amount of time to rebuild the surface. If you restrict the points that the surface uses to a given area, the surface rebuilds faster and the drawing size is smaller.
The exercises in this tutorial demonstrate how to insert a relatively dense LIDAR point file into a surface, but restrict the amount of data that is actually used.