The discrete elements method (DEM) has been widely used in the past decade to study a wide variety of granular systems. The use of numerical simulations constitutes an interesting alternative to the experiment as they can shed new light on a phenomenon as they can overcome experimental obstacles. A lot of granular phenomena can be studied in 2D or with a limited number of grains but the peculiar phenomenon of axial segregation (or banding) is 3-dimensional by nature and requires a large number of grains. Only very recently has it been made possible to simulate 3D systems on a large scale. This highlight reviews recent work on this topic and attempts to show what knowledge is gained from DEM numerical simulations. The perspectives on the future benefit of this method as well as the challenges it faces are discussed.