It depends on what you're trying to do with them. Some things to consider:
Are you trying to nail a quarter size "x" ring at 25 meters against some of the best shooters in the world or are you hunting moose?
How long are your shafts when cut? (The shorter they are cut the straighter they should become)
How fast are you pushing them? (The harder they are pushed the more sensitive they become)
How well do you shoot? (If your form causes a 4" group, you're not going to see a 1/2" difference in point of impact caused by the arrow.)
I think the average deer hunter could shoot +/- .006" arrows and kill just as many critters as the next guy, but if the next guy is standing on the tournament line shooting .003's, I want to be shooting .001's.