The Interdimensional Traveler: A Full Body Character Design - ZBrush Creature Design: Creating Dynamic Concept Imagery for Film and Games - page 162

higher subdivision level, ZBrush will sometimes lose details from your mesh. The mask effectively frees
the details while you delete hidden faces.
3. Step down to the lowest subdivision level and press the Tool ⇒ Geometry ⇒ Delete Hidden button to
remove the hidden faces. ZBrush will preserve your details and your subdivision levels while deleting the
unused body from the secondary arms ( Figure 3-66 ) .
Figure 3-65: Drawing a masking marquee around the secondary arms (transparency is on)
Figure 3-66: Delete hidden faces on the second set of arms to permanently remove the hidden body geo-
metry we don't need.