The most common use case of the above feature is Quantity Discounts. You can let the user enter the desired quantity and calculate the price based on the quantity-range value set by you in the element properties.
As shown in the image below, you can set different prices for different quantity ranges, $5 for range 1 to 49, $4 for range 50 - 99, and so on.
Then, in the formula, you can retrieve the quantity-based price through the label name, i.e. "Quantity", and the actual value entered by the user in the number input through "Quantity[actualvalue]". So, the final price can be calculated by the formula - Quantity*Quantity[actualvalue]