Function available in CINEMA 4D Prime, Visualize, Broadcast, Studio & BodyPaint 3D Chamfer Options Tool
Radius defines the radius of the chamfer. If Flat is enabled, the chamfering is linear.
To be more exact:
Flat disabled — each new point has a tangent created to round the chamfer. Flat enabled — no tangents are created and the spline runs linearly between the two new points.