Create Coordinate System
Command - PrB_CreateCoordsys
If you are looking for an object that calculates 'intermediate' geometries, then you should definitely use the Plane helper geometry. The plane object is far better suited for that purpose.
A coordinate system is a type of UCS object in the drawing. This object has no practical use for the output of the drawing itself (this object will never appear in a bill of material or workshop drawing).
This type of object is almost never used, except for baseplate-like connections.
The baseplate connections use this coordinate system to stick the macro to the drawings' World coordinates.
As you have already seen, each 3D drawing has such a coordinate system that is fixed on the World of the drawing and that you cannot remove.
The baseplate connections have geometric rules to this world coordinate system.
Whenever the baseplate macro is copied or inserted, the geometric rules are fixed to the World coordinate system of the 3D drawing.
This ensures a fix to the WCS coordinates across all drawings.