FDTD simulations enable us to predict the physical parameters of nanostructures, which will theoretically give the best experimental LSPR signals. This information is crucial to optimize sample fabrication and to avoid wasting a lot of time and money. Simulation is also essential for controlling and calibrating the various parameters of fabricated nanostructures, and for understanding certain modifications to the samples, such as adding of Cr or ITO adhesion layers, covering nanostructures with dielectric layers, or thermal annealing... Finally, FDTD calculations are helpful for interpreting LSPR experiments and better understanding the adsorption of gas molecules on Au LSPR nanosensors and the catalysis of chemical reactions.