ZBrush, especially ZBrush 3, can be used for high detail sculpting from a base mesh created in another package or now that the retopology tools have been introduced, you can create a base mesh in Z, sculpt and retopo to make a clean, animate-able mesh for use in an external package. Z also fills a texturing capacity quite admirably.
With 3d layers, allowance for multiple editable objects within one document, retopo functionality, and rapid design visualization, the question isn't really what is Z good for, it's why haven't you tried it yet?