Hi Massimiliano @mazinga ,
So you are using a blender Version from before the Course 😉
For anyone answering this question: these are now in the category Edit Modifiers.
As far as I know, those are sometimes used to get unrealistic reflections, but https://cgcookie.com/courses/pothead-create-a-hard-surface-character-in-blender shows a really good example to ‘fix’ some reflections with the Transfer Normals Modifier…
Those Modifiers are not being used very often though; it’s especially pretty rare, that you need them for realism, I’d say…