There is nothing wrong with holding your breath for a few seconds before exhalation, and your pelvic floor muscles also need to be conditioned as you progress in your chi-kung, tai-chi or meditation practice. I'm not at issue with this. The problem is, to satisfy impatient students, some chi-kung practitioners are saying "hold your breath and squeeze your anus" as quintessential chi-kung. I even heard a popular master in Hong Kong saying when you got minor flu, do a few times of inhale, hold your breath and squeeze your anus, and exhale and it will cure your flu! If you would ask my advice, I will say putting on your Rockport and doing some walking in the park can generate more chi than "hold your breath and squeeze your anus". And for minor flu, better take the doctor's advice of talking one or two tablets of paracetamol before the flu becomes full blown.
Holding one's breath and squeezing one's anus though are one of those key techniques in Pranayama of Indian Yoga practitioners. They are respectively called kumbhala (the art of retention) and bandha (bondage). These are however high-level yoga pranayama techniques and not to be practiced by novice without supervision. The holding of breath in yoga is a advanced technique for increasing the potential power of prana (or chi) and it can cause undue strain to both the heart and the nervous systems if practiced incorrectly. Bondage is a technique used together with retention to direct prana (or chi) towards desired channels.
In both tai-chi and Taoist meditation, a holding of breath for any length of time is not encouraged except what is absolutely necessary for the mind to direct the chi along chi-channels. More natural, and safer, methods are used.