List the customers who purchased (or have not purchased) a particular product (eg product X)
This is useful for targeted marketing.
List the customers who purchased a certain product (eg product X) and show the customers who have not purchased this product X (also filter between certain dates). This is useful for targeted marketing when you want to promote certain products to a customer group. Can also be used for "now we have an addition to the product you bought" that is also targeted marketing.