In my experience with learning and teaching I-Liq Chuan, I have noticed that a lot of time is spent training the point of contact.  Once the basic understanding of body unification is achieved, training can quickly progress to framing movements in terms of the point of contact.  The point of contact provides a context for movements and serves as a training aid which guides the training progression.

The way I usually introduce the the point of contact is as a physical link for coupling force into your opponent.  To affect your opponent’s structure (or control balance via the structure), you need a link to couple your force into your opponent.  The most straightforward way to do that would be to grab at the point of contact.  The coupling of force can also be done without grabbing.  The touch contact needs to align to solid structure (i.e. bone), and the body must unify to the point of contact.  When those two conditions are met at the point, usable force can be coupled into the opponent’s structure.

The nature of the point of contact is dynamic.  Outside of static demonstrations for teaching, the point of contact will be constantly changing.  This necessitates attention to the point of contact to perceive the present conditions at the point.  The act of focusing the attention to feeling and adapting to the changing point is itself training.  Like breathing in sitting meditation, paying attention to the point of contact is a mental focus tool during partner training.  Spinning to flow at the point is largely a mental exercise.

Probably most importantly (at least from my point of view as an instructor), the point of contact provides a feedback tool.  Whether a student understands body unification or movement applications can be felt from touch.  The same touch at the point of contact can be used to provide kinesthetic feedback.  Once the correct touch has been demonstrated and felt, the student has a diagnostic to gauge whether the body alignments and movement modifications are correct.  The point of contact serves as a training diagnostic for both the instructors and students to assess and correct alignments and movements.