What does the Standard version do?
The Standard version motivates customers to spend more. Every time they add something to the cart, it shows them how much more is required to reach the goal.
For example, if you offer free shipping at $100 and the customer adds a $79 product to the cart a message tells them they're $21 away from getting free shipping.
What does the Premium version do?
The premium version allows you to offer motivator messages only to specific countries (helpful when offering free shipping, for example). It can automatically add a free product to the cart when a user reaches a goal amount, and it allows you to schedule motivator messages to start and stop automatically at chosen times.