Projection milling techniques are a robust and easily understood method of generating 3D toolpaths. They work by taking a pattern of curves and projecting points from these curves onto the surfaces of the part.
Advantages
Robust
Handles overlapping surfaces well.
Good for multiple surface manufacturing.
Allows specifying planar stepover distances or scallop heights for finishing.
Surface normals are not considered for the manufacturing computation
Disadvantages
Poor handling of nearly vertical surfaces
Does not handle vertical surfaces since they are invisible from above.
See Restrictions of projection milling techniques for more details.