Why do some pharmacies say they can't refill your controlled substance schedule 4 until three days?

The pharmacies are more and more getting strict with narcotics. The DEA have started to come and audit pharmacies that fill the most narcotics. They are holding the pharmacist's accountable. There is no law says they can't fill it the day, usually 7 days in advance, that the insurance will cover it. But, it is highly suggests that they shouldn't be filling narcotics until the day the person will run out.
Most pharmacies aren't that strict. Also, if the 'consumers' that usually run out before they're due to get their refill/new script, and they'll have to withdraw for a few days or maybe a week will stop taking more than what is they're prescribed regime.
Basically, they think that the withdrawal will motivate you to take your meds as is prescribed by your doctor & you won't run out.