The modelling of crystal surfaces, both in equilibrium and during growth, is now at a stage where the relation between surface structure and crystal quality are accessible for future studies. The classical point of view is that the roughening transition marks the transition from step growth to rough growth with qualitative changes in the growth rate and the morphology. The surface-melting transition marks a change from solid-like to liquid-like surface layers. This enhances the kinetics and will decrease the anisotropy of equilibrium surface properties. It has been shown that surface melting may also lead to a linear growth law. Slightly speculative arguments are given to illustrate how surface roughness and softness are related to morphological instability, impurity incorporation, mother-phase inclusions, dislocation formation and stacking faults.