Taichi short forms developed after 1956 are shorter and faster than the old forms, and they become nothing more than low-impact aerobic dances. They do not have any healing effect as the taichi old forms (30 minutes a day), unless you do 30 sets of short-forms in one day (see link below for explanations). But, who would have time and strength to do 30 sets of fast taichi or aerobics?
http://www.researchgate.net/publication/260640603_The_30-Time_Start-Stop_Interval_Training_For_Internal_Organs_-_An_aerobic_exercise_for_the_brain_and_other_organs
Article Tai Chi improves balance and mobility in people with Parkinson disease
Article The 30-Time Start-Stop Interval Training For Internal Organs...