To use guide bushings on your plate, you have to have the bit centered in the plate opening so they will be centered in the bushing. I can't think of any other reason for centering other than this, so if you don't plan on using bushings, don't worry about it. If you are going to use bushings, want to center the bit and the pre-drilled plate won't allow you to center; Simply enlarge the screw holes/recesses in the plate to allow some wiggle room for the plate to be centered.
Fort Worth, Texas
City where the west begins.