Yes some pros do use some drag brake, whereas others actually allow the car some roll at idle. The reason for drag brake is so that your car will slow without moving your trigger to the full brake position and also as Domit mentioned it will bring your nose down slightly just by letting off the trigger.
I would say a high percentage of the pros that use drag brake come from the electric scene. Many people from the "brushed" motor days are programmed to use some drag brake.