ADP 3-90, page 85

Enabling Operations 31 July 2019 ADP 3-90 5-5 by mutual agreement—the time to transfer command. They disseminate this information to the lowest levels of both organizations. 5-20. A commander’s reasons for conducting a passage of lines are to—  Sustain the tempo of the offense.  Maintain the viability of the defense by transferring responsibility from one unit to another.  Transition from a delay or security operation by one force to a defense.  Free a unit for another mission or task. The headquarters directing the passage of lines is responsible for determining when the passage of lines starts and finishes.