When would it be appropriate for a company to lower its allowance for doubtful accounts as a percentage of its receivables?

At no point any provision for doubtful debt is suggested as a percentage of receivables.
Provision is made on the actual fact plus a certain amount of provision can be made if any receivable goes due beyond180 days.
If any receivable is overdue for more than60 days, a partial provision is recommended in consumer industry.