The PolyPaint system in ZBrush allows painting on a model’s surface without first assigning a texture map. A texture map can be created at a later time, and the painted surface can be transferred to the map. PolyPainting offers significant advantages compared to standard workflow:
The resolution of the texture map need not be decided in advance. This is particularly valuable if you find you need more detailing on an area than you thought you would. Instead of repainting a new, larger texture map, you can simply transfer the existing surface painting to a new, larger map, with no rework necessary.
Similarly, the UV unwrapping need not be fixed in advance. If one unwrapping proves unsatisfactory, simply create a different unwrapping and transfer the surface painting to that map.
Removing UVs from your model frees up system resources and allows you to work with more polygons.
Texture artists can begin working in high resolution, before UV's have been assigned – or even before the final low resolution mesh has been created. Whenever the artist and model are ready, this PolyPaint is converted to a texture map with a single button click. Not only does this allow texturing to begin much earlier in the pipeline, it also adds the ability to change a model's geometry or UV mapping at any time without sacrificing any texturing that has already been done.