Why The Smith chart is a polar plot of the complex reflection coefficient overlaid with normalized resistance and reactance circles. Moving around the chart's constant-SWR circle corresponds to moving along a transmission line, so you can transform a load impedance to the impedance seen at any point on the line, and also work out matching networks and SWR. That impedance transformation along a line is its core purpose.
Watch out Radiation resistance, radiation patterns and propagation predictions all depend on antenna geometry, ground and the ionosphere, none of which the Smith chart models; it only handles impedance and reflection along a line.
Smith chart = transmission line slide rule: impedance, SWR and matching, never patterns or propagation.