abstract: In this talk I will illustrate new questions, at the interface between Calculus of Variations and Geometric Measure Theory, motivated in a broad sense by the more applied machine learning community. More specifically, I will deal with second-order variational problems in the setting of functions with bounded variation and study the extremality properties of continuous and piecewise affine functions in the unit ball of a suitable energy, used as a regularization term in the applied community. In connection with this, a fine approximation result by piecewise affine function has been investigated. Papers in collaboration with C.Brena, S.Conti, S.Aziznejad and M.Unser.