  We address the importance of the modern theory of orbital magnetization for
spintronics. Based on an all-electron first-principles approach, we demonstrate
that the predictive power of the routinely employed "atom-centered"
approximation is limited to materials like elemental bulk ferromagnets, while
the application of the modern theory of orbital magnetization is crucial in
chemically or structurally inhomogeneous systems such as magnetic thin films,
and materials exhibiting non-trivial topology in reciprocal and real
space,~e.g.,~Chern insulators or non-collinear systems. We find that the modern
theory is particularly crucial for describing magnetism in a class of materials
that we suggest here $-$ topological orbital ferromagnets.
