Zhan zhuang can be used as an excellent diagnostic tool for one's structural form (or posture) for an experienced practitioner or new practitioner, provided that he can relax and can focus on balancing his internal chi. A teacher (sifu) will be beneficial to see it happening. Once a person's structural form can be visualized, its perfection, or in most cases, its imperfections can be seen and areas of focus in training can therefore be identified.
The process is simple. With the guidance of an experienced teacher (personal guidance is sufficient for experienced practitioners), a student is to move into the zone between asleep and waking up, with his eyes closed, always tending towards the sleeping side, while maintaining the ability to stand up in a zhan zhuang form. Points (fingers and hands) stretched while body relaxed should be observed. After being in the zone, a student will initially experience an imbalance of chi (if he can actively relax his muscles into deep-dead feel while keeping his stretched parts as slightly stretched as possible to maintain a chi-gradient). A teacher's chi managing help will be beneficial (but not essential) for most students. Such help essentially means managing a student's chi-flow through elbow chi-touch by his teacher.
After ten to fifteen minutes, a student is asked to calmly open his eyes, keep his body form, and keep his chi balance. He will be surprised to find out that his natural chi-balanced posture is far from perfect. Bravo, he starts to "know himself" (a tai chi lingo), and has a visual road-map for training.