I understand that zBrush is a program commonly used by game designers and animators, but the reason for this eludes me. Unlike programs such as Maya and 3D StudioMax, models made in zBrush cannot be animated and it is mostly used for organic figures, so with that being said what do they usually use it for?
With its multi-million polygon support and real-time sculpting features, ZBrush comes as close as you can get to the feeling of working with clay. That makes it possible to quickly create models that would take forever or be outright impossible in other software.
Additionally, it is capable of high frequency detailing, which let you easily create displacement and/or normal maps for your animation-ready models so that they have much more realism when rendered by your animation software.
Finally, it actually CAN be used to create animation-ready models thanks to features like ZRemesher.
I recommend checking out these links:
http://pixologic.com/zbrush/industry/
http://pixologic.com/interview/artist/
The first gives general information concerning how ZBrush is being used in specific industries. The second is artists and studios talking about why they use it.
garycinderella wrote: What is zBrush used for?
I would say practically everything, at this stage of its development.