Generally, this occurs in vehicles that have disc brakes. The pulsing happens when the brake pads squeeze the warped rotor. Other causes can be loose or worn suspension or steering components, but warped rotors are almost always the cause. Don't be fooled, by a pulsing pedal if your car has Anti-Lock Brakes. Pulsing indicates that the ABS system is working on newer cars that are so equipped.
Rotors have a service life determined by how thick they are at the time of servicing.
Some rotors can be turned, others cannot. If in doubt, call your dealer or refer to a manual to check the specifications. A good habit to get into is to have your mechanic take a quick visual inspection of the condition of the pads whenever he's under the car. It only takes a minute. Rear brakes, if they are drum type, require some disassembly to inspect them, but they must also be periodically inspected.