The min and max power setting provides a range of power for the laser to work within. Many times the machine will need to move the head at a speed other than what you specified. The most common reason for this is to change direction, for example, when cutting a corner. If the min and max power are set the same the laser will continue to output the same power even when traveling at a different speed. Providing a min and max power allows the laser to reduce the power down to the minimum whenever it needs to reduce the speed, allowing it to be more consistent.