Its hardly a "respec" though - your vocation is like a job from Final Fanstasy Tactics, you are expected to switch them frequently and are rewarded for doing so. Each vocation has a "rank" (1-10) that is retained when you switch between them (so if you are a Rank 8 Fighter and switch to a Mage, you'll be a Rank 1 Mage but can always switch back to being a Rank 8 Fighter). Your overall level and exp don't change when you switch vocations though, so if you are level 30 and change vocations you are still level 30 and thus still have a lot more HP, Strength, Magic, etc. than a level 1.
Part of the motivation for switching is that many skills can crossover between classes that share the same weapon type, and there are also passive "Augments" which you can use on any vocation once they are learned. For example, you may want to get an Augment from a Strider that increases your stamina and then use it while you are a Mage. Although still quite viable, a player that switches Vocations and mixes and matches Augments is likely to be better off than one that just sticks to a single vocation for the entire game.
I agree one save is stupid as hell, but just wanted to clarify that switching vocations isn't something you should feel you need a different save for.
Another advantage changing vocations bring is that each one has a different stat bonus when your character levels up. Here's the breakdown up to level 100 :
HP = health, Stam = stamina, MD = Magick Defense, Def = Defense, MA = Magick Attack, Atk = Attack (Strength)
Levels 1-10:
Fighter: HP+30 Stam+20 Atk+4 Def+3 MA+2 MD+2
Strider: HP+25 Stam+25 Atk+3 Def+3 MA+3 MD+2
Mage: HP+22 Stam+20 Atk+2 Def+3 MA+4 MD+3
Levels 10-100:
Fighter: HP+37 Stam+15 Atk+4 Def+4 MA+2 MD+1
Warrior: HP+40 Stam+20 Atk+5 Def+3 MA+2 MD+1
Mystic Knight: HP+30 Stam+20 Atk+2 Def+3 MA+3 MD+3
Strider: HP+25 Stam+25 Atk+3 Def+3 MA+3 MD+2
Ranger: HP+21 Stam+30 Atk+4 Def+2 MA+3 MD+2
Assassin: HP+22 Stam+27 Atk+6 Def+2 MA+2 MD+1
Mage: HP+21 Stam+10 Atk+2 Def+1 MA+4 MD+4
Sorcerer: HP+16 Stam+15 Atk+2 Def+1 MA+5 MD+5
Magic Archer: HP+20 Stam+20 Atk+2 Def+3 MA+3 MD+4