Rachana Prakash this is a very good question! Perhaps something that if I was wiser, I would have added to the article. Primarily, it would be so that you cannot mutate object values.

const PlaneActionTypes = {
  Up: "[Plane] Up",
  Down: "[Plane] DOWN",
  Left: "[Plane] LEFT",
  Right: "[Plane] RIGHT",
}
PlaneActionTypes.Up = "[Plane] DOWN";
// this works
enum PlaneActionTypes {
  Up = "[Plane] Up",
  Down = "[Plane] DOWN",
  Left = "[Plane] LEFT",
  Right = "[Plane] RIGHT",
}
PlaneActionTypes.Up = "[Plane] DOWN";
// error cannot re-assign value