You can be a level 50 Archer with nothing else but the game is designed with multiclassing in mind.
A level 50 Archer with the Bard job added to it and a bunch of abilities learned from other classes will be significantly better than a straight level 50 Archer.
It's just how the game was meant to be played.
The game has not been clear because it doesn't matter yet, but with a minimum of research, you can find out all the infos about it.
Here: http://finalfantasy.wikia.com/wiki/Arche...IV%29#Bard
A level 50 Archer with the Bard job added to it and a bunch of abilities learned from other classes will be significantly better than a straight level 50 Archer.
It's just how the game was meant to be played.
The game has not been clear because it doesn't matter yet, but with a minimum of research, you can find out all the infos about it.
Here: http://finalfantasy.wikia.com/wiki/Arche...IV%29#Bard