Ok, NUCKLES has the right idea, but is saying it in a forceable way. let me help him out.
at -1, you will notice no difference, at -2, you might notice some. (i ski my pow skis at -2)
If you have a pow ski, i would recommend mounting them at center. they will ski better in the park this way, and with a wide-ish ski, with a solid shovel, early rise, and a super soft symmetrical flex, they will be fine and fun in everything else.
Depending on your mix of park and pow, pick either -2 or more (-2 is about as close as i would go to center if you are skiing any more pow than a 50-50 split with park) or dead center. at -1, you get no benefit over -2, or dead center. its literally one centimeter.
So, QUICK REVIEW:
Mostly park: I recommend center
At least 50% not park: i recommend 2+ cm back from center