I found tools to paint all sort of material setups, spec, color, reflection and much more. But I dont know why I should paint normal maps there.

I just found out that there is a HD sculpting mode, where ZBrush creates even more subdivisions dynamically only for the region where you sculpt. So you can even sculpt with virtually billions of polygons, not only millions. This is very impressive:
http://www.pixologic.com/docs/index.php/HD_Geometry

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