As its name implies, this method produces programmed points connected by straight lines in machine tools as cnc milling machine, whether this distance is close or far apart. Motion can be achieved in any number of axes simultaneously. As an example.of this, if we consider a machining centre's axes configuration, it can produce linear interpolation on the X, Y and Z axes for spatial point movement and B and C for rotating motions. 

Thus, on a 5-axes machine tool it would be incrementing feeds at differing rates to allow for contour machining to be undertaken. When a contour is to be machined using linear interpolation, then the higher the number of individual points present, the closer this approximation is to a true curve . To achieve this feat, the controller in cnc machining center, lathe machine requires a high data processing ability and using such methods it is possible to theoretically control the cutter path around any complex shape, notwithstanding the geometrical limitations of the cutter orientation to the workpiece. 

A major problem with using this interpolation method, is that when contour machining, the part programs tend to be of vast block length. Incidentally, this was one of the major reasons for the demise of NC punched paper tape as a storage medium for of the reasons why complex contours.

The example can be in the following link, have a look and show your opinion: http://www.cncdatan.com/milling/cnc-milling.html