Geodetic transformation performs a cartographic transformation from a coordinate reference system to produce a geographic coordinate system (that is, latitude and longitude) that is referenced to the same datum as the source coordinate system. Geodetic transformation paths concatenate individual geodetic transformations to use when a direct transformation is not available.
For example, you might have two drawings: one that uses geographic coordinate system A and one that uses geographic coordinate system C. If you have only transformations for A to B and A to D, there is no direct transformation from A to C. If there is a transformation defined from B to C and from D to C, AutoCAD Map 3D toolset has to choose one of these. It might use the transformation A to B to C. However, you might prefer that it use A to D to C.
To ensure that the transformation path A to D to C is used, define that transformation option as a specific geodetic transformation path. Once you define a path, AutoCAD Map 3D toolset will always use the one you defined. You can add paths that use their original definitions, and you can add the inverse version of the paths.