Taijiquan's health benefits are quite clear:
Improve health (e.g., body resistance) and blood circulation, balance and coordination, etc. If you want to see some pictures of what the Chen-style forms look like, do visit Sifu Paul Chou's website (http://www.chentaichi.com )
For posture, please visit www.cloudwater.com
Taijiquan for self-defence
Yes, one can learn taijiquan for self-defence, although it may take a fair number of years. Push hands will be a necessary component for developing sensitivity and the ability to stick, neutralise, etc. Apart from that, fajing drills and zhanzhuang (standing qigong in various postures) will be important as is chansigong (silk reeling exercises).
Some insights:
The following quotes are excerpted from Sifu Hawkins Cheung, who studied wingchun kungfu under Grandmaster Yip Man (both men are small in size):
"When I saw Yip Man stick hands with others, he was very relaxed and talked to his partner. Sometimes he threw his partner out without having to hit him.
If you take an analogy of a big car facing a small car, you can see that the driver of the small car doesn't have much of a chance. The small car driver has to shut off the engine or interrupt the shift to first gear of the big-car driver. obviously, the big car can just run over a small car and destroy it.
When Yip Man faced a larger opponent, his skill was so high that he would shut off his opponent's engine or never let it start. When you're old, you have to adapt this way to survive. With my small size, I had to learn this method...
By Hong Kong standards, he [Bruce Lee] was a big car."
Source: http://www.hawkinscheung.com
Sifu Cheng jiefeng has this to day about push hands:
"When a student first trains in push hands, I have them practise the single push hands, softly, making 200 revolutions on each leg. This training goes on for sometime until I am sure the student is able to relax more. When the student shows the ability to relax, and keep the qi down in zhangzhuang as well as push hands practice, then we explore pengjing (ward off energy)." (Source: Inside Kung-fu, April 1994).
