Every posture has applications with regards to martial arts. You just have to find an instructor that is adept in explaining it all. Don’t settle with teachers that are fixed in one structure. An instructor who is skilled enough can teach you wide assortments of defenses and attacks.
Practice is a durable way of perfecting a specific move. You first start with your techniques. Through the practice of Push Hands, you can be trained about dynamics of the body and balance. It can be curtailed like that of the Judo enthusiasts.
Once Push Hands techniques are learned, you can naturally convert it as a form of martial art self defense or in an offensive manner. Now, if you already have joined any kind of martial art before, Tai Chi can be pretty effective in reconstructing your skill and enhancing it into something that can be translated as an improvement and a challenge.
Even though it was already stated several times now, people who are attracted to Tai Chi never consider it as a kung-fu type but as a form of relaxation and meditative process. And some would rather follow the crowd than make a jump out of the ordinary and consider other options that the exercise can be applied to.
Practically, Tai Chi is not a martial art BUT can be applied as one. You can’t be a black belt by being an expert in every Tai Chi strategy and movement, though the principles of fundamentality are always present. But if your teacher is really good, he or she can make you learn specific Tai Chi techniques and add-ons that will make you a better martial artist. Like the one with Push Hands.