The role of slag in ladle metallurgy and tundish is discussedstarting from thermodynamic considerations of equilibrium/non-equilibrium states between slag and steel. Some interesting steel grades with different deoxidation philosophy are chosen as examples. Physical aspects concerning therole of stirring, slag properties e.g. viscosity and interfacialtension are examined as well. The title question is discussedand evaluated based on theoretical considerations andcomparison with modelling experiences and industrial data.