Digital Creator School has a look at creating bevels and rounded edges at render time using the Arnold Round Corners node.

No doubt bevels and rounded edges ground a hard surface model in realism. A beveled edge will catch the light and help to define the forms. Creating soft round corners at the geometry level can lead to higher polygon counts in the scene. The thing is, you don’t necessarily need to bevel every edge physically. Most renderers will offer a rounded corners tool that lets you do it at render time, and Arnold is no exception.

Lucas Ridley of Digital Creator School fame breaks down how this works in Maya using Arnold. The node appears to round sdges by modifying the shading normals near the edges of the geometry. Using the node with hard surface models where bevels have not been modeled to simulate a round beveled edge, thus saving valuable modeling time.