We discuss the influence of elastic and inelastic events, which are gas-pressure dependent, on various processes of interest in the operation of glow discharge (GD) systems. In particular, we consider the generation, in the dark space near the cathode, of the fluxes of energetic particles that bombard the cathode; in this process, inelastic collisional events dominate. The transport and thermalization in the plasma region of the energetic particles emitted from the cathode is then evaluated. In this stage elastic collisions are the most relevant events. The deposition at the anode of energetic and thermalized particles is discussed briefly. We consider the following types of energetic species: (a) energetic electrons; (b) energetic background gas ions and neutrals that sputter the cathode and, after being eventually backscattered at the cathode, strike the anode; and (c) sputtered particle fluxes on their way from the source towards the substrate. The theoretical tools available for these kinds of studies are discussed, in particular analytical methods and Monte Carlo (MC) simulations. We briefly touch upon some applications of the results obtained on etching and thin film growth processes.