In order to do any physical activity in the correct way, one must go through the process of "slow-motion", while maintaining other essential requirements. Take playing a musical instrument for example, say learning how to play a piano. In the beginning one must do it slowly, but maintain the correct rhythm, and above all "do it right", i.e. striking the right notes! With more practice, one can then do it at the required tempo. And it goes with the learning of every new piece. Is this all about tai-chi being done at slow-motion? The answer is negative!
To understand tai-chi's slow-motion workout concept, one must first appreciate the most important requirement of doing tai-chi. I'm talking about Song (松). The English translations include: loosen, release and relax. And its meaning is all-of-the-above. For those who don't know Chinese, no need to worry. Most Chinese are as much at a loss with its meaning as you!
I just put it definitively first: The objective of doing tai-chi in slow-motion is to Song (i.e. loosen, release and relax) all our joints - and in particular our shoulders' and pelvis' ball and socket joints.
Question: is it then the same as doing stretching, or like doing yoga-asanas? The answer is negative. Yoga-asana and usual stretching can loosen one's tight joints but will NOT strengthen them. Actually, if one has weak joints, one is advised NOT to do too much stretching or yoga-asanas (check my post for details HERE)
In order to both strengthen and loosen one's joints, one can do tai-chi, and do it in slow-motion, and focus on the four ball and socket joints mentioned above first. The method is simple. When doing tai-chi, focus your mind on either your shoulder joints or your pelvic joints (in advanced stage: both). While keeping yourself mindful there, and while doing slow-motion, try to rotate your joints as wide a path as possible, paying particular attention to firstly overcoming the blockage (or seek the path of most resistance), and secondly DON'T avoid excessive joint-movements in the beginning.
By seeking the path of most resistance, one will automatically slow down when doing tai-chi - rather than "forcefully" slow it down which will likely result in a loss-of-concentration.
In particular when turning the shoulder joints, due to existing blockages, oftentimes a practitioner has to move his elbow up and outward in order to do a big wide turn inside his shoulder joint. That would "violate" the usual requirement of "drop your shoulder and hold your elbow down" 沉肩墜肘. It is essential to "violate" this requirement in the learning process!
Enjoy your slow-motion tai-chi!