Architectural Illustrators can use the shape, along with the other element form, to generate visual forces that direct our eyes as we view the rendering.
Many shapes, such as the triangle, have a general body movement that points in one specific direction. Obviously, not all shapes are equally important in contributing to movement, for some provide more of a directional force than others. Compare, for example, the 'forceful" rectangle to the "stable" but less directional square.
As a general rule, the longer the shape, the greater the directional force.