When you tighten fasteners, such as head bolts, main studs, rod bolts or anything that requires precise torque, they can be off a lot in torque if some of the bolts have oil on them, or if the hole you are going into is not lubricated properly.  Because of this, ARP has developed a lube to make sure that all of your torque readings are the same- making all of your fastened parts consistent in torque.