Let me use your Black Magic class as an example.
Sure, you can stop at the level your spells are at. In a way, you are using your points efficiently, since you can use different jobs while still casting Black Magic spells once that level has been mastered. But if you continue on with the Black Magic job, you can gain the passive skill MP+30%.
All jobs grant you some perk for mastering them completely. Whether it is the use of passive skills, the ability to equip different weapons or armor on classes that do not normally have them, or spells to use while playing as a different job. I won't spoil you on what each one does, though. So, continue the story and earn the AP necessary to master those jobs.
Bookmarks