This is usually used as a transition and only reads the first frame. It then outputs the first frame for every frame after it. Much of the outcome depends on the window size. For 44100 audio a window size of 4096 seems to work best. Downward shift requires larger window sizes and upward shifting requires smaller window sizes.
Voices shift better than music.
Getting good reverb is more of an artform even for the most automated signal processors. The output consists of an initial signal followed by many reflections. As the reflections move out in time, a lowpass filter is usually applied with decreasing cutoff frequency. If more than one track is attached to a single reverb plugin, the reflections for both tracks are swapped to simulate stereo. Simulated stereo is capable of using a separate CPU for each track.