As someone who was formally trained in 3D Animation, I can tell you that a lot of conventional 3D is painstakingly slow to build. It involves box-modeling line-by-line. Zbrush is a program that allows the artist to just start sculpting 3D geometry without any of the slow box-modeling techniques, allowing you to complete a model much faster. This is just a small video of me using the program to show how an artist, even freestyling, can make something pretty darn cool fast.