The Giraud does not "disfigure" the case mouths, IMO. It cuts the most beautiful inside/outside bevels you will ever see. Bullets seated in cases trimmed/chamfered with the Giraud go in absolutely like butter, and every single case will be trimmed exactly the same. It does exactly what a trimmer should do. Do the bevels have to be as deep as they are in order to function? No. However, the more important question is whether having a nice deep chamfer as is cut by the Giraud in any way impairs precision/consistency. I believe the answer to that is also, "No." In fact, the uniformity and consistency to which the Giraud trims and chamfers cases actually promotes precision, IMO.
In the most general sense, because the blade is a notched "V" shape, adjusting it side-to-side will minimize/maximize the inside/outside chamfer, one at the expense of the other as spife7980 mentioned. It is actually a little more complicated than that, as the shape of the "V" notched blade will allow for more complex adjustment of the bevels and trim length, but doing so requires a good eye and an extreme amount of patience to get it "just right".