A model made from a Sphere or Cube will inherit the edge-flow of its origin. This model of a Dragonhead has a very bad edgeflow because of that.
When it comes to creating assets for games or animation, good topology is essential. Without it the textures won´t look good, and it will be a nightmare to animate.
Further more the mesh will have a too high resolution to be of any use at all outside ZBrush.
If you are simply making a model in ZBrush and don´t have to worry about Polygon-budgets and edge-flow, you may not need to retopo your model. But it is highly recomended.
When you are rebuilding a mesh, the workflow is simple.
First load you tool so it is stored in memory. Then load a ZSphere. Expand the Rigging menu and click Choose mesh and click on the stored tool.
Next bind the mesh to the ZSphere. If you want you can move the Sphere, and resize it. Most of the time though, this is not necessary.
Next you need to expand the Topology menu and since we are building a brand new topology, ckick Edit Topology. This will hide the ZSphere from view.
Go into Draw-mode and CTRL-click on the place you want the first polygon to begin. If you intend to make the new mesh symetric, hit X to get mirrored modelling.
ZSpeheres are made up of chains of connected points that in turn combine to create faces between the vertices. As you click your way following the shape of the underlying mesh, hit the A key often as this will preview what the new mesh will look like.
It will also expose errors. Make sure you always CTRL-click whenever you click on a new startingpoint for a new face. If you don´t you risk getting distortions and star-shapes, because ZBrush continues to add vertices based on the starting-point.
Keep working your way over the mesh until you have either covered the whole thing, or leave out the parts you don´t want. In my case I removed the eyes and the mouth since I wanted to create these separately.
The mesh I have in the end may not be the best topology ever seen, but now it is useful and editable in a whole new way.
During the retopology process, you can allso move vertices by changing ti Move Mode. Select the point you want to move and change the position.
I hope this tutorial has been helpful.