This has been available for some time now, as you’re probably aware.
Rather than leave an icon on the screen (which may not follow the art as it gets moved), it saves projection data in the art object’s dictionary, which can be read again when needed. You can also save the projection as a preset in the menu.
It’s very important to keep in mind that an Auxiliary Projection is not like a projection in the Projection panel. The Projection panel is meant for working in three planes of the overall illustration and requires a vertical axis that’s actually vertical. The Auxiliary Projection panel addresses ONE unusual plane within the drawing that is neither left, right, top, nor bottom: it is the FRONT face. You can detail that face by moving, extruding, or projecting art between orthographic and the auxiliary axonometric FRONT face only. If you need to switch to an adjacent face, you can use the flyout menu to rotate it 90° on the X or Y axis.