User Guide > Rendering and Render Setup > Shading > Shading Windows and Editors > Hypershade > Hypershade menu bar >
Options > Clear Before Graphing
If Clear Before Graphing is on, selecting a node already in the Work Area and performing a Graph Input and, or Output Connections operation clears the Work Area before the new graph is drawn. If Clear Before Graphing is off, the same workflow adds the nodes in the new graph to the Work Area without removing previous nodes.