There are problems that may arise in between services and for a list of their tell tale signs. See troubleshooters for more details
If your brakes are making a scratching sound when you brake then it is probably due to worn brake pads/shoes that expose the head of a rivit which in turn scratches the disc/drum surface. You will need to take action immediately as this can cause permanent damage to the braking surface and result in a less effective brake and a pulling to one side when braking
Remember Worn brakes take longer to act reducing the ability of the car to slow down increasing the braking distance. Brake pads are made from materials that increase friction. When this material wears down and the rivets are exposed then the only contact is metal to metal which produces less friction and much less stopping power.