Back of a pack is helpful to explain how the product is important to users/buyers and the benefits of that product. When users make a purchase decision, when they see a pack in a mall, most of the time they don’t have anybody around to explain the product benefits to them, in such a circumstances back of the pack plays an important role.
In website context, when users make purchase decision what are the pack back elements are as follows
- rating
- recommendations
- reviews
I think Amazon.com is a very good example of using pack back elements in a website.