Tai Chi, when done right, has many, many health benefits and most importantly it positivity affects one's homeostasis - it regulates the autonomic nervous system which in turn affects all of the body's systems.
One very obvious way Tai Chi relates to playing cello is because it uses principals of empty and full, also known as yin and yang. If you think about playing a melody, you want your weight to be in the finger that is playing, with the rest of the fingers essentially being "empty", or to put it another way, not loaded with excess muscle tone. Of course, this is easier said than done.
This is why I use the term "Cello As a Practice". When I practice, I monitor my state of mind as much as anything else, and the easiest way to do this is to be aware of my breathing. I do not "breathe with the music". Instead, I breathe when I need to. I am aware of what my diaphragm feels like when it is moving freely. When it is stuck, it is because I am not allowing the exhale to happen fully.
There are many elements of Tai Chi that go into my playing and the art of performance.