In one sense a PES can be thought of as a conceptual tool for aiding the analysis of molecular structure and chemical reaction dynamics, and such an analysis makes use of the concept of a PES in the following way. Once it is possible to evaluate the necessary points on a PES, the points can be further classified according to the first and second derivatives of the energy with respect to position, which respectively are the gradient and the curvature. Stationary points, that is, those points with a zero gradient, have some physical meaning: energy minima correspond to physically stable chemical species and saddle points correspond to transition states, the highest energy point on the reaction pathway, that is, the lowest energy pathway connecting a chemical reactant to a chemical product.
See geometry optimization for more information and Computational Chemistry for deeper discussions of how the concept of a PES is used in practice.