When you create a product discount, you have the option to duplicate and hide that product if you wish. This means that you can create a copy of your product and apply a discount to only the copy, without affecting the price on the original product. This is useful if you want to offer special discounts to certain people, without advertising the sale price on your site.
For example, you can use our Product Upsell app to offer a buy one, get one 50% off deal. Where if a customer purchases something, they then get the 2nd for half the price. Obviously you don't want to discount the original product's price because you don't want everyone to get the sale price - only those who buy an original one. Therefore, you would duplicate it and hide it from your store and only offer it to those who qualify. This feature even removes it from the site search results so you no longer have to worry about people finding it who shouldn't!