Percentage is being used for computing the profit margin, mark up, discounting,  and forecasting business plan either for the growth and reduction of plan , based on the sales history. fraction for efficiency, sales against plan, rate of return of investment.efficiency for collection against plan. decimal is also applied in computing each inventory cost or net cost from suppliers when a discount are adjusted depending promo volume plus additional volume. decimal is likely applicable especially the first in first out cost posting, and capital  posting especially the quantity wont tally a whole capital cost.