Distinguishing between the gripper edge (leading edge) and the tail edge (trailing edge) is critical because only one of these margins is used to secure the sheet for registration during the initial pass. The gripper edge is the fixed reference point for all layout coordinates. However, in a Perfecting System, the sheet is flipped, and in many configurations, the tail edge becomes the leading edge for the second side. If the paper is not perfectly square or the Imposition did not account for this flip, the front-to-back alignment will fail, resulting in a misregistered final product.

Properly identifying these edges allows prepress teams to place color bars and pull-guides in the correct positions. While the gripper edge is non-printable, the tail edge is often where "ghosting" or mechanical slur is most visible. By managing both edges strategically, printers can optimize their substrate usage and ensure that finishing processes, like folding and trimming, align perfectly with the printed content on both sides of the sheet.