This is actually the third BojiLite strike, Chau Chui, but I number it as the second drill because it is easier to perform than Sao Chui in terms of power.
As with the Yum Chui every move must be expressed clearly. Outwardly, it seems like we are training how to strike but there is more to it than meets the eye.
A drill that only trains one thing at a time is not a very good drill because then we would need a lot of drills to train different things. It is much more efficient to have a drill that can train several things even if some of the things we are training is not clear at first.
On the other hand, to have a complex drill to train several things can be counter-productive because it makes the learning more difficult. In Chinese martial arts drills can be designed to look as if they are teaching one thing when they are actually teaching several things.
Usually, these non-obvious things that a simple drill teaches will only be revealed once the beginner can perform the drills to meet basic requirements. In this way, learn more by training less.