Mainly it is personal preference unless the string is going to be for a finger shooter. If for a finger shooter it needs to be served in a certain direction depending if it is for a left hand or right handed shooter. It has to be in a certain direction for a finger shooter so that when they draw the bow, the center serving will always be in a tightening twist under their fingers. If you served them the wrong way the serving will work itself looser each time they draw the bow.