You see the payment fee separately from product cost
Before, you tracked a sale's profit as just price minus product cost, while the fee from a card, a split payment, or a card reader disappeared inside that math unnamed. With the calculator separating the two amounts, you see how much each one takes from the sale. This lowers the odds of closing an installment sale thinking the profit would match a cash sale.
You stop treating the profit number as more complete than it is
Before, you logged the calculator's result as the sale's final profit, even when packaging, delivery, a discount, a freebie, or a loss had also eaten into it. With the habit of naming what was left out, you start keeping two pieces of information per sale: what the calculator showed and what still needs to be subtracted. This lowers the risk of deciding based on a number that looked bigger than it really was.
You compare sales with different payment methods more easily
Before, you compared a bank transfer sale with an installment sale by guessing the fee in your head, which usually came out wrong. With the calculator applying the right fee for each payment method, the results are ready for a direct comparison. This helps you notice when pushing bank transfer or cash changes what's left.
You get a record of what each sale left out
Before, even when you noticed a sale had delivery, a discount, or a loss, you left that cost unrecorded anywhere near the calculator's result. With the habit of listing excluded costs next to the result, the store builds a history of sales with the real profit and what's still left to subtract from it. This helps you look back later at which sales were actually worth it.