Greetings..
Just something i have noticed over the years.. Wuji or Zhang Zhuan is a pretty good indicator of a person's level of dedication and discipline.. by insisting that we begin each class with at least 5 minutes of standing meditation i have watched many student's dedication and discipline evolve and some deteriorate..
From a personal perspective it is a super inventory of current physical, mental and spiritual status.. one can sense Qi trouble spots, can correct almost imperceptable alignment inconsistencies, can calm scattered thinking, and raise the spirit.. all this while cultivating Qi.. not to mention regulating breath.. in my personal practice i begin with Taiji Diagram training for +/- 5 minutes prior to standing to activate Qi so i can more easily sense its presence and movement..
Much wisdom has been posted regarding the necessity for solid grounding, and standing meditations are excellent disciplines for sensing and developing one's connection with the earth.. internal arts are foundationally dependent upon grounding (rooting) to attain any reasonable level of proficiency or power.. try standing in neck deep water where your grounding is compromised by buoyancy and water applies resistance to every move, remaining grounded during movement is quite difficult (but a good practice).. Dr, Yang Jwing-Ming offers an excellent training tool in his "standing on bricks" routine.. stand bricks on end then do your standing meditations and silk reeling while standing on the bricks.. he says, and my experience agrees, that you learn to project your Qi downward past the bricks to eastblish balance and rooting..
For me, standing meditations are as essential as the form itself.. it is the Wuji that supports Taiji..
Be well..
TaiChiBob.. "the teacher that is not also a student is neither"