Increment If Unique Function
This function will increment the value of the property by 1, if the value passed into the function is unique to this property and has not been used before.
E.g. for a property "Total Unique Products Ordered" which is configured to set the value when the "place order" event occurs, and the function is passed the "Order.ProductID", if this product has not been purchased before then the value is incremented by 1.
Another use for this is counting the number of emails a customer has opened because an email reference is unique.