its not rocket science - the distributor has an rotor that times the ignition to the cylinders, that rotor is fit to a shaft, that shaft is not actually a solid connection to the engine, its a spring loaded connection on top of a shaft. its held steady by weights and springs. When engine rpm increases the weights spread and the timing is advanced.
That mechanism requires greasing or repairing (weight or spring replacement if they are worn out) the breaker place is the plate where the contact points (point) is mounted to - this plate is pulled in by the vacuum advance - if the vacuum pot is bad the advance wont work, if the plate bearings are jammed it wont work.
the difference is night and day in engine performance.