Using variance in statistics allows you to see how individual numbers relate to each other within a data set. A variance can be used to leave leeway when figuring the cost of something, such as labor rates, sales volume, sales quantity, and materials quantity.
Over the course of a job, labor rates can fluctuate, so you would have to allow a variance for the possible rise and fall of the rate. If you use gold in your pricing for the jewelry, you will need a variance because of the price of gold changes at a minimum daily.
One day gold could be $1,000.00 per ounce, and the next could be $1,500.00 per ounce so that you would need a variance. The variance is useful because it can mean the difference between loss and profit projections.