Quote Originally Posted by Droxxic View Post
SNIP
You are looking at it the wrong way.
Take Whitemage for example. To become a Whitemage you must have a level 30 Conjurer level AND level 15 Arcanist on the same character.

You can switch back and forth between the jobs without any drawback (Besides skills being on CD when in the field). Once you are leveling a job you only gain XP for that job.
You retain all levels you gained in previous jobs. Simply switch weapons and you will switch to that job.

My advice? Get a little of all caster levels or a little of all fighter levels. Some skills can be used on other classes (crossclass skills).
For a healer, Swiftcast from Thaumaturge is a godsend for example.

Hope this clears things up a bit