As the points begin to open, current will jump across the air gap. The current will carry a small amount of metal from one point surface to the other. This is known as "pitting". The condenser will try to keep the voltage constant as the points open and absorb the current preventing the "arc" to help stop the pitting. I have seen cars that have not had the condenser changed in many years and I doubt they are still functioning. The car still runs fine, so people don't change them. The old rule was new points, cap, rotor, condenser every 12,000 miles. Remember the metal in the distributor cap wears too. Also the point arm rides on the distributor shaft which opens the points and as the arm wears the point gap gets smaller and smaller.