You can try an experiment: tap Yiming (EX-HN 14) on the head, and you will feel a pulse corresponding massage shanghai to the tapping at Taichong (LR 3) on the foot.
Answer: Random tapping with varying force and speed is used to stir and smooth the meridians.
Different parts of the body are connected and must be connected.
The random tapping smoothes the meridians so that Qi and blood can circulate freely.
If people get hit unprepared, they always feel more pain than otherwise. For the random tapping, it is the same dynamic. It stirs up the body more.