All rotating your tires does it help them wear evenly in relation to each other. You certainly don't need to but your tires may or may not wear unevenly thus requiring a new set earlier than later. Rotating isn't always an (or at least isnt an easy) option depending on your setup.

I run square setups with directional tires. I just rotate front and rear occasionally. I don't bother with side to side.

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03 3.0i mt
89 325is