I used
Arthur Relaford (DUR 16, ST 85, Cy Young-caliber pitcher) as a dominant Setup A for several seasons, got 120 outstanding innings out of him every season.
It was a mistake-- I would now use him as an SP with PC 70/75, get about 170-180 innings. It's not that Relaford, personally, would be that much more effective in that way; his ERA would be somewhat higher as an SP due to in-game fatigue, and his leverage was quite high in the SuA role. It's that élite pitchers who CAN give you 5 innings every 5th day don't grow on trees, and when you get one you have to use him that way. It's much easier to fill out a championship quality staff if you start him.