In Wujifa, (without going into the philosophy of the triangles) Zhan Zhuang is first practiced to discover structure, then connection. This is a very functional place to begin, as it calibrates the body and the mind to be able to work with more advanced practices.
I asked my Wujifa brother and I discovered that after all my years of reading and note taking in class, I had only a vague and very, method-based understanding of the principle of functionality. This is how I understood our conversation and how I now understand the principle of “functionality”.
The Wujifa triangle(s) is a graphic representation of what it means to be functional. How can I apply the first triangle in my Zhan Zhuang practice? My body functions optimally when there are equal levels of Structure, Relax and Balance. The more I refine this first triangle in my body, the more I feel internal connectedness; what is felt by others as internal strength. This is the meaning of "get the body functional". Where one corner is more exaggerated or diminished than another (or other two), then the whole is not functional, or can be said to be dysfunctional.
A principle can be applied to various frames or contexts whereas a rule only applies to a single frame or context. The Wujifa triangle(s) represents a principle and as such, may be applied in various frames or contexts.
For example, in a martial arts context, a beginning martial artist may learn techniques/rules/methods. For example, if your partner executes this technique, then counter with this technique. As the practitioner progresses, s/he may come to understand the underlying principle of the various techniques. Wujifa takes the “learn the principle first” approach so the body responds in a way that maintains functionality: structure, balance, relax.
As always, my understanding is subject to further refinement. Thankfully, there is no end to learning...