What is the healing effect of Zhan Zhuang? The answer is both excellent and minimal. It all depends on how mindful you are and how you proceed from there. Mindfulness is at the heart of all internal disciplines, which include most if not all Eastern spiritual practices, chi-kung, and internal martial arts. They differ according to their respective subject of mindfulness.
I always recommend anyone interested in such practices to start with zhan zhuang (or standing meditation). Through a soundly-coached practice of zhan zhuang, a practitioner can quickly recognize and have an immediate experience of an internal feel - an internal "thing" (物) or an internal chi (气). And only after one can identify this internal feel, one then can mindful cultivate it at whatever location and in whatever way that is required in a particular discipline. Without this internal feel, as the old saying goes, everything will just be academic!
In conclusion, zhan zhuang is one of the doors for one to enter into this arena of internal mindfulness. And I recommend zhan zhuang as the best and easiest door for anyone who is interested to enter the arena.
Another useful tool? As simple as taking a cold shower!