“When working inside ZBrush, everytime I start modeling something from Z-sphere. It is one of ZBrush’s cool features that enables fast and intuitive modeling of low poly objects. Also what I like with this tool is, you can constantly check the outcome of your ZSphere form on how it looks when turned into mesh by pressing “A” key on your keyboard.”
http://www.cgarena.com/freestuff/tutorials/zbrush/dinosaur/dinosaur.html