It is important to note that the Pro and Lite point of sale experiences differ slightly. With the Pro version of the POS, you can set up triggers for things like buy one and get one free, and discounts based on how much someone spends. These add-ons aren't available with POS Lite, though.
With POS Pro, you can also offer your customers a greater range of options when it comes to accessing your products, including buy online and ship to customer solutions. You can also offer online purchases and in-store pickups.
With Shopify POS Pro, you'll be able to strengthen relationships with customers in other ways besides integrating with email marketing tools and social media. Based on what previous customers bought, you can make product recommendations when you collect customer data.