Basically, disk brakes work better and work when they are wet. Drums don’t. On the other hand, it’s hard to mechanically clamp pads to a disk when the car is parked whereas it is easy to pull drum brake shoes into solid contact with the drums using just a cable. That’s why many vehicles have drums on the rear and disks on the front – disks to stop the car, and drums to hold it once it is parked.