Matcaps are a great feature in ZBrush. They are realtime and they bring the sculpture to live.
Introduced with Zbrush 3.0 Matcaps have the benefit to bake light, color and properties
into the shader.
I created many Matcaps over the years. One reason is that the right Matcap brings you
in the mood for the subject you are sculpting on, another reason is that artists work
long hours on a sculpture and a good matcap prevent the eyes for getting tired too fast.
Changing Matcaps during the work also helps to see the work with fresh eyes.
Also in combination with BPR you got fast renders for presentation.
There is a fine balance to create a digital representation of a real world material or an
unique and interesting approach that works in ZBrush especially for a sculpting Matcap.
I got repeatedly asked for my Matcaps, so I put together a Set of some of my classic RS_Matcaps
for sculpting and some for presentation and made them available for free.
Have fun sculpting!
Cheers
Ralf Stumpf