While shapes are supported on Excel and PowerPoint Office.JS API, it's not the case of the Word API. Please allow us to: Create a new shape Edit the shape color and add a background image Add ...
Shapes are also useful in creating book covers for on-demand book printers. Being able to create shapes and size/position them on a page (and in groups?) makes it possible to support multiple cover types (softback, hardback, different publishers, different spine widths) from one document. This would require manipulating shape layout (position and size) as well as textbox layout and properties.