Magic Boost is an offensive attribute, and affects a character’s ability to inflict damage with magical attacks and spells. Characters with a higher Magic Boost attribute will inflict more damage with magical attacks and spells.
Classes like Sorcerers and Spiritmasters, who rely on magical attacks and spells to inflict damage to their targets, tend to have the most Magic Boost, though Clerics and Chanters can also benefit from more Magic Boost.
A high Magic Boost attribute is important for classes that inflict magical damage. Physical damage classes, like Gladiators, Assassins, and Rangers, receive little to no benefit from Magic Boost.