If you have to tell something about why do you prefere sculpting in zbrush…:spin:
Am I right in guessing that you are asking why someone would prefer to work in Zbrush over say other sculpting software?
If so because it offers high levels of detail, a tablet focused interface, tons of topology tools, shadowbox, a huge set of brushes and most importantly 3d painting on top of it all. Its masking capabilities are awesome and there’s really nothing on par with it yet, even Blender…though I have to admit I have seen some spheres get up to some pretty darned high polycounts in Blender…until its used for actually hardcore asset creation though its hard to use over zbrush.
These links alone can show why one would prefer zbrush:
blender scultping is getting pretty good, but I still prefer Z-brush. apart from what SaintHaven mentioned, I also prefer noisemaker to muching around with displacement modifiers in blender (mostly, depends on how UV reliant it is). Really though, its a collection of lots and lots of little features that all make things that little bit easier.
Because ZBrush is the best sculpting program there is 
Fantastically fast interaction with up to 100 million polys on my computer, great texture projection and painting tools, a tool shelf that feels very much like traditional sculpting (tools on the left, extras on the right), built-in turntable and session recording tools, ZSpheres, ZSketching, polygroups, QRemesher, Dynamesh, amazing boolean tools, fast, accurate reprojection, transpose tools, shadowbox, easy creation of normal/displacement maps, very quick rendering with GI. I could probably go on for hours. It’s just a really great piece of software. As much as I love the integration of sculpt tools in Blender it doesn’t even come close, and as many times as I’ve tried to get into Mudbox over the years I just keep going back to the original.
I like it because it’s $700. Free software really isn’t that good…