Molecular dynamics (MD) simulations are now widely used to study both dense and dilute granular flows, which often coexist in the same system. However, this simulation technique has to be used with care when the forces are non-conservative. We briefly discuss the artifacts which then may arise. The example of granular chute flow illustrates how MD simulations may help to understand the microscopic processes underlying the macroscopic flow properties. In particular, it is shown how sterical constraints in the flow can lead to an insensitivity of the mean quantities to material properties like the coefficient of restitution.