Passengers may despise checked baggage fees, but a new study shows they actually help reduce departure delays. The study was published in the August issue of peer-reviewed journal Management Science.

The study’s authors analyzed more than 9 million flights between May 2007 and May 2009 and compared delays at airlines before and after the implemented checked baggage fees. They controlled for factors like weather, aircraft age and number of passengers on a flight to determine the impact of bag fees alone.

Many travelers, as the study notes, assume bag fees lead to more people carrying bags onto planes, a practice that can actually lead to flight delays because the plane takes more time to load — especially if those overhead bins fill up, slowing down the boarding process.

But passengers aren’t aware of the authors’ so-called “below the cabin” effect. Baggage fees have indeed reduced the number of checked bags, which speeds the loading and screening process.

“Our study provides an empirical support that the checked baggage fee policies were associated with an improvement in a key airline performance metric, on-time departure performance,” the authors wrote.