Transformations between datums can be accomplished in a number of ways.
For many geographic coordinate systems, multiple transformations exist. They may differ by accuracy, or purpose. By default, AutoCAD Map 3D toolset automatically performs a transformation (either a Geodetic Transformation Path or a Geodetic Transformation) between two datums. But with Geodetic Transformation Preference, you can specify a different transformation for a user use or one drawing use only.