It’s a bit tricky to answer that question.
When you change the CPlane, you change the local coordinate system.
You can never change the “world” coordinate system.
If you don’t change any CPlanes, only the “Top” CPlane is the same as the world CPlane - all other CPlanes are local coordinate systems.
All default CPlanes have their origin at the world origin.
With any CPlane active, when you create geometry (e.g. a point) and put it at “0” (short for 0,0,0), it will be placed relative to the local coordinate system.
To force creating geometry relative to the world coordinate system, you can pre-fix typed coordinates with “w” - e.g. “w0”, or “w1,5,0”.