For flexibility and efficiency.

I come as BRD for Turns 1-3 and BLM for Turn 4-5
Our other BLM comes as WHM for Turn 2 Enrage

I never queue for more than 5 mins for CT, ever (not counting the constant party member withdrawals) as I can change as necessary.

More gil from roulette as I am always on the 'needed' role.