Unlike aikido, which is completely a martial art, tai chi is at least as much a meditation.
When I was involved in poor theatre, we did some tai chi. The purpose, as with the other physical disciplines, was the focus, and centering, that it required, and developed.
This is not just a mental thing. The whole point about acting is to, well, act. And you want people to look at you. The quality of movement that comes to those who work at tai chi is the thing.
There is no partial movement. There is nothing, from the smallest flexing of the smallest finger, to the largest bending of the whole body, that doesn't come from the center--the solar plexis, the chi.
I regret not continuing this discipline, but, even today, I still feel the benefits.