You can merge two pieces along a common edge into one piece.
To merge two pieces:
Move the pieces so they are in edge to edge contact. You may find this easier if you select Snap to Edge on the Horizontal contextual menu.
On the Main toolbar, click Select.
On the Horizontal contextual menu, ensure Pieces is selected.
Move the pieces so they are in edge to edge contact. You may find this easier if you select Snap to Edge on the Horizontal contextual menu.
Select both pieces. (Press Shift while clicking both pieces.)
Go to the Context view, in the Actions section.
Click Merge.
VStitcher merges the two shapes and pastes the merged shape on top of the two source shapes. Drag the merged shape, so you can see both.
You can now edit the newly created merged piece or the original pieces as you want.