Most students' heart rates average around 130 bpm during class. In this posture your heart rate can go to 150 to 170 bpm - for that amazing 10 seconds.
At the same time there is an incredible stretching action happening with the arteries surrounding the heart, like stretching a rubber band. There's this stretching going on at the same time that the heart rate is increasing. Then everything is released and you can actually feel this sensation of the blood flowing through your whole body.
The stretching and improved blood flow helps to reduce and diminish plaque within your arteries. Giving you a mini heart attack so you don't have to have one later!
In addition to the cardiovascular benefits, this posture builds balance, firms the hips and buttocks and increases the flexibility of the shoulders.
There really is only one thing to do when practicing this posture. Once you step forward, come down immediately parallel to the floor - T like Tom - and hold for at least 10 seconds. That way you won't miss any of the benefits from this posture.
One of the best ways to learn more about the postures is to read Bikram's "Beginning Yoga Class" book. Attend class 3 to 5 times weekly to put your learning into action and make your body smile!