When the receding lines are drawn to half size, the drawing is known as a cabinet projection.

In oblique projections, one of the object's principal faces is parallel to the plane of projection.

If you are sketching an ellipse in an oblique drawing, you can block in the enclosing rectangle and sketch the ellipse tangent to its sides.

If a complicated pictorial is needed, it may be easier and more accurate to create a 3D model than an oblique drawing.

In CAD, oblique drawings are difficult to create because you cannot use snap increments or draw similarly to drawing on grid paper.