When working with a solidworks drawing, should I delare

Dim swModel as As SldWorks.ModelDoc2
Dim swDrawing As SldWorks.DrawingDoc
and
Set swModel = swApp.ActiveDoc
Set swDrawing= swModel


or

Dim swDrawing As SldWorks.DrawingDoc
and
Set swDrawing = swApp.ActiveDoc


The second one seems to be simple, however, I got errors sometimes

Could anyone please explain this to me

Thx, ChrisSolidworksApi macros