In magnetizing the magnetic domains inside of a magnet are aligned with the magnetizing field. If the magnetizing field strength is high enough, all the domains will be aligned and the magnet is said to be magnetized to saturation. Magnetizing to saturation is usually recommended as only then are the magnetic properties of a magnet achieved. A partially magnetized magnet is unstable and easily demagnetized.
Figue 1: HPMG have china biggest magnetizing machine.