Fundamentals of the three-dimensional spatial harmonic analysis (SHA) approach are reviewed, and the advantages of a fast-converging formulation versus the initial SHA formulation are emphasized with examples using periodic plasmonic nanostructures. First, two independent parallel versions of both formulations are implemented using the scattering matrix algorithm for multilayer cascading. Then, by comparing the results from both formulations, it is shown that choosing an advanced fast-converging scheme could be essential for accurate and efficient modeling of plasmonic structures. Important obstacles to the fast parallel implementation of this approach are also revealed. The results of test simulations are validated using the data obtained from a commercial finite-element method (FEM) simulations and from the experimental characterization of fabricated samples.