There is no direct content where you say "good that whe had that specific class with us". That would exclude other classes and would lead more to situation, like in WoW, where people with specific classes wasnt invited in group content anymore.
There are only sometimes situation, where it was good, to have a certain class with you. And that happens mostly, when players failing the mechanic ("good that whe had a paladin, who protected and healed the dd, after the other DD and healer died by the boss", "good that whe had a Red mage/summoner with us, who ressurected the healer or other party member, after the healer died/leaved the battle field").
The only difference should be, how the classes are played. But even that should be only small differences to each other (be it fast meele [monk, ninja, reaper -with his shroud-; Viper] vs agil meele [dragoon, Reaper -like drg for his mobility, and dislike reaper a bit, because his reach feels short-] vs slower, but stronger meele [samurai, who feels slower, has barely any mobility and feels to have a short reach], or differently Flair of caster [classic wizard in Form of blm, using summons as summoner or be a painter] or tank with differently focus [paladin, to protect other vs dark knight, who is doing dmg] or differently stil of healing [remove dmg or prefent dmg]).
But it should be never happens, that you need a specific class for the specific content (like, that you NEED specific the white mage, because the dmg is so fast, that only he could heal it away).