Effectiveness
Contributor: Emcy
In my opinion, a party in Final Fantasy isn't complete without having a Black Mage (or Wizard) along. Usually, how people set things up is that they designate a fighter (or two depending on the party max), having one healer and then finally, one that can use offensive magic. It doesn't have to be a class that purely does black magic like the Black Mage but still, most will chose a character who can do some.
Not only is having a character who can do offensive magic really cool but it is also very useful along the way. In the FF series, you will always encounter an enemy (or two hundred) that has high physical defense but very low magic defense. This is where having a Black Mage comes in handy. With the powerful and plentiful spells, these creatures can be reduced down in size within a matter of moments or careful strategy.
Having such a diverse range in their pockets, Black Mages can also exploit elemental weaknesses to help the party defeat an enemy a little quicker then normal. This helps out even more on boss battles or important battles that you just can't afford to use up items on by sticking around too long.
It's a short explanation, I know, but in my opinion, that pretty much sums it up. Black Mages are very useful to have in your party and for an easier and more effective play through, I'd suggest always having one on hand if they're available.