Just like some people used to say " I like coffee when the bean is dark and oily", others believed a good roast had to do with a smooth surface appearance. Indeed there is a point where the coffee expands enough and the browning reactions have sufficiently completed that the surface no longer seems mottled in color and texture. People used to feel this correlated to a Full City roast. The issue is that different coffees will expand and brown differently, and roasting any coffee until it looks a certain way ignores the fact that how the coffee tastes is the most important thing. Nobody drinks a bitter cup of coffee and says, "I don't enjoy this terrible brew, but in fact I know it's good because the beans looked so smooth."