Meh. As has been said, forcing your characters into one job facilitates storytelling. Rather than relying on a more general, heroes try to stop villain's scheme of destroying/taking over the world plot, you can actually drive the story with the characters. Indeed, I think many consider FFIV to have one of the best stories in the series.

But really it comes down to personal preference. In the FF series so far I've found I've enjoyed the extra dimension of customizing, "building" and experimenting with my characters over more restricted "interactive storytelling" like that found in FFIV. It's not that big a deal for me though; I do appreciate the change up--if the games all played the same they never would have gotten so many people to play all of them.