This shows you how many chocolates you have, cancels the bunny aura, opens any eggs in your inventory, and uses the speed boost basket toy if you have it, all with one button, just keep spamming it as you run around looking for eggs.
The bunny transformation doesn’t increase your movement speed at all, and it prevents use of the Eagger Basket toy that increases movement speed. Pretty annoying that they haven’t at least allowed use of the toy while transformed, since it happens so frequently while egg hunting.