Is there a benefit in leveling a new class compared to rolling an alternative char?

[Niwashi]

Downside to alts is having to grind the same content twice.

Disadvantage: got to play the game again.

It's odd how often I see people list getting a chance to repeat all the one-time-only content as being a disadvantage, whereas I see it as being by far the biggest advantage of why people would want to make new characters. I for one like the game's main storyline, so like being able to play through it more than just once. Even a lot of the side quests are pretty fun as well.

I do have a question that relates to this topic. IS it best to take your first class all the way to 50 before branching out to others or does it matter?

Aside from a brief detour by level 30 to bring up your job's secondary class to 15 so you can unlock your job, the rest is mainly a personal preference issue. (Oh, that's except for crafting classes. If you're interested in crafting, it's better to level all of those up together.)