The main purpose of this legislation is to make a tax provision permanent that allows businesses to account for depreciation, amortization, or depletion when calculating the limit on how much interest they can deduct from their taxable income. This is important for businesses as it can significantly affect their tax liabilities and overall financial health. The key provision of this legislation is the permanent extension of the allowance for depreciation, amortization, or depletion in determining the income limitation on the deduction for business interest.