Retarding the cam will move the power band up slightly but will raise the rpm at which the power band starts and finishes. Advancing the cam on the other hand will lower the power band of the cam. Even if you degree your cam and find out it is straight up at 0 you will never know how your specific car combo will react until you do advance or retard it with real track or dyno numbers.
I actually run a 224 roller with 2 degree advanced to bring the power band down a a little. I've never run a before and after so I don't really know if it is helping or hurting. Just figured to advance it to increase cylinder pressure at a lower rpm.
In a perfect situation you should pick a cam and degree it straight up at 0.
Rule of thumb - If your car increases mph after retarding the cam then your combo needs a bigger cam. If your car increases mph after advancing the cam then you needs a smaller cam.