The mechanics and dynamics of biological flagellate swimmers are complex, yet for populations one can easily expect tens to hundreds of millions cells to be present. Thus there is a pressing need to rationally and accurately simplify the dynamics of flagellated swimming cells to facilitate the development of large cell number simulations. Here, we will review elements of the mechanics for single cells before considering how the individual swimmer may be rationally simplified to enable population level modelling, and the application of this framework to understanding sperm clustering also highlights the perils of averaging to obtain population models.