The reason that bharatanatyam dancers beat their feet and move up and down the stage for a full 8-10 seconds or so after a jathi (pure dance sequence) was for a few reasons:
1. To move in the procession when they were dancing outside in a parade like setting.
2. To move back to hear the musicians (who, unlike now, where they sit to the left of a dancer on stage, used to stand and play behind them).
Now you know.