wiesiek wrote:..." how it can be used in training..."
You can not use it in training, you train It undirectly for removing all >internal blockades<,
this gives you uninterrupted internal connection, which allows you to use technique as it was designed.
Very nicely expressed in Wiesiek-idiom
Plus it's likely part of the general health-promoting effects of Tai Chi, when the art is trained properly. Not only for motor functions but also for metabolism and general organ function.
Maybe a comparison to jogging/running is useful. Jogging will usually improve your breathing, causing you to breathe more deeply and increase lung capacity. But when you go running you don't usually focus specifically on your lung capacity - you simply run, you aim to move in a supple way while pushing yourself a little. The better breathing is a good side effect. When you train Tai Chi properly, putting the classical principles into practice as well as you can, it will have the good side effect of freeing up your fascia. Maybe you can start to perceive this more directly, which is nice feedback that you're on the right track, but it will probably happen by itself.