Why do we use ZBrush and why is it so widely used in the game and film industry? Because it is very good for creating highly detailed models in a very short time. This may sound trivial, but it is very sought-after and if you have seen the amazing detail on some creatures in Avatar (film), The Lord of the Rings (film) or Gears of War (game), you'll know how much this adds to the experience. Without the possibilities of ZBrush, we weren't able to achieve such an incredible level of detail that looks almost real, like this detailed close-up of an arm:

But apart from creating hyper-realistic models in games or films, ZBrush also focuses on making model creation easier and more lifelike. For these reasons, it essentially tries to mimic working with real clay, which is easy to understand. So it's all about adding and removing digital clay, which is quite a fun and intuitive way of creating 3D-models.

Yet it is important to know that ZBrush is a very specialized tool, so it is mostly used in conjunction with other 3D Software to animate or export the models into a game engine, for example. Still, specialization comes along with efficiency and you will be amazed how easily we can realize our ideas with ZBrush in no time.