This tool lets you quickly draw basic procedural objects down onto the XY plane in world space. This is useful for quickly creating test scenes for various purposes by interactively drawing primitives directly into the scene in a fast intuitive workflow.
Each object type has 2 or 3 different steps to draw.
With a cube it will first draw out a cube on the XY plane by holding down the left mouse button. When you let go of the button it will then change the height of the cube. Doing a final click will finish off the drawing of the cube.
Other objects have similar multi-click workflows. Pressing and releasing the left mouse button until the object drawing is finished.