Every fluid which gets through a channeling has any facons a very small speed near walls and even no speed on the wall because of the viscosity of the water. This is the limit coat (limit layer I don't know the exact term) phenomenon and it always appear in any situations.
In order to improve turbulence and break this limit coat the wall of maze should be lined(crossed off) perpendicularly in the direction of drainage of the stream to favor the appearance of mini-vortex which improve the thermic exchange wall/fluid..
So when I see nice waterblocks with walls very shiny and flat, it is not good for the thermic exchange, it could be improved by damaging the state of surface of walls. But I think people who buy waterblocks want the most beautiful block very clean and very shiny
. You have probably see this technics of "raw state of surface" on some aircooling systems to favor turbulence....