The reason for a bad debt provision is that, under the matching principle, a business should match revenues with related expenses in the same accounting period. Doing so shows the full effect of a billed sale transaction in a single accounting period. If you were to not use a bad debt provision, and instead used the direct write off method to only charge bad debts to expense when you were certain that a specific invoice was not collectible, then the charge to expense might be many months later than the initial revenue recognition associated with the billing. Thus, under the direct write off method, profits will be too high in the period of the billing to the customer, and too low in the later period when you finally charge some portion or all of an invoice to the bad debt expense.