Yes, it is only for half-court. The effect is that basically the opponent with the ball is double teamed. That is why speed and athleticism are so important to this defense. There is a lot of shifting and movement by the defense to quickly cover the ball handler.
I use +/- just like any other defense. If an opposing team is heavy with 3-point shooters, then I go to a + setting. If they are weak, then I use the - setting.