First, your understanding of CDA is wrong. The definition of CDA does not include the optimization of ILS approach phase. After the plane arrived at the final approach location FAF, it intercepted the ILS glide path signal and began to descend along the ILS glide path at a 3-degree glide angle. There is no step-down flight at this stage, but a fixed FPA flight.

Secondly, the cascade descent method, which is widely used at present, is mainly characterized by adjusting the flight altitude after passing a certain waypoint and flying horizontally to the next waypoint with altitude change. The advantage of this method is that it enhances the flexibility of setting the minimum obstacle height of aircraft, and it is very cheap for airport site selection and air traffic control flight program design. In addition, the pilot adopts this flight mode, and the control of the decline rate of the aircraft in the province is more stable. Before arriving at ILS, the plane has resumed its stable flight attitude.

Finally, regarding the advantages of CDA over step descent, during the whole flight from cruising altitude to intercepting ILS altitude, CDA flight adopts the whole process of setting the thrust of idle descent, while step descent needs to increase the engine thrust to maintain flight stability during the plane's level flight, so the most remarkable feature of CDA is that the fuel consumption in the whole flight is greatly reduced. At the same time, the plane descends at a fixed angle close to 3 degrees FPA, so the real flight speed is higher and the flight time is shortened. ATC controllers can better predict the scheduled arrival time of the plane, reduce the scheduling pressure of controllers, make the flight sequencing more reasonable, shorten the flight interval and reduce the delay.

If this person is interested in CDA, I recommend you to read the relevant literature of AIAA. The research on /CDO in foreign countries is very mature. Welcome to exchange and study.