An exposition of the effects of sampling on the controllability characteristics and the Kronecker invariants of the plant and the input matrices of sampled-data systems is presented. In particular, the effect of sampling period on the feedback matrix for time-optimal control of sampled-data systems is investigated in detail, and it is shown that different classes of systems produce different response characteristics as the sampling period becomes large. Also, simple expressions for A(NT) in terms of A(T), and B(NT) as a function of A(T) and B(T), are derived. These expressions are computationally attractive and therefore facilitate the study of the effect of sampling period on system behaviour. By applying these expressions, the effects of sampling period on the feedback matrices for time-optimal control of three classes of systems whose open-loop plants are asymptotically stable, marginally stable, and unstable, are illustrated by numerical examples.