A Piggy Bank is simply a way for customers to organise their savings into logical segments that make sense to them, and simultaneously make it slightly difficult to see what balance is inside (balances can be viewed after a 30 second delay)..
You may have specific goals that you are saving towards, such as a house deposit or new car, or you may simply want to put money aside for emergencies. It is up to you whether you create Piggy Banks or not, and how you use them.