Probably money and dealing with stupid drivers. It is also easier to deal with drivers whose only thought is miles"I want miles" they can't understand freight lanes, why some loads pay more than others. Drivers don't understand that when they take a good paying load into a dead area why they can't get a good paying load out. Think they get tired of trying to explain how freight is priced?

There is much more to consider when you run percentage. When you run mileage all you need to concern yourself with is how many miles you can do in a day. Running percentage requires you to understand what it takes to make a profit on a load and whether there is a decent rate coming out of where you are heading.