A qualitative knowledge of how a continuous distillation column is expected to react to a physical parameter variation is often required, both in simulation and in practical operation. The topic is discussed in this paper with the aim to indicate some simple predictive rules concerning the steady-state variations, both under open- and closed-loop control. The binary distillation in conventional and non-conventional columns is examined in detail; some indications are also given for the multicomponent distillation in conventional columns. Geometrical constraints and asymptotic solutions are the basis for the adopted approach.