Let’s say you had a data file where each point in the file had a color associated with it. In VTK, the points would go into vtkPoints, the colors would go in vtkPointData. Hopefully that clears up the relationship between vtkPoints and vtkPointData. Of course, VTK can associate a lot more than just colors with the points and cells.
If the authors had called the class vtkPointAttributes or vtkPointProperties, it would be less confusing. But vtkPointData is the name they chose, and we just have to live with that.
If you’re only inserested in geometry and topology, then you don’t need use vtkPointData or vtkCellData.