NCG CAM machines using triangulations as standard, which are quick to calculate and check against for gouge free machining. True surface machining is optional for users to select, should they wish. Machining the surfaces spaces the points in the NC Tape file more uniformly, giving a better / smoother machine movement on some machine tools. However, the calculations to ensure the machining is gouge free will take longer in most cases.
The better the surface finish means less hand polishing, which saves time and money, it also reduces any mis-match / flash caused by polishing rolling/belling corners.