My first example would be entering carrier claims, credits for discounts, and price adjustments for a famous Tractor Company. When the dealer places an order most of the time the price and discounts are calculated automatically however a PROMO is being offered if the dealer orders so much for a short period they get an additional 20% off the invoice. Once they place the order they will send me the order number and I will calculate the amount of discount given and added to the order. The invoice was 3840.92 and I gave a 20% discount. 3840.92 X 0.20 = 768.18 which is 20 %. Percentages are useful because we tend to have a better understanding of something out of than fractions and decimals