Cheese is salted for two primary reasons. The first reason for salting cheese is to slow down or stop the bacterial process of converting lactose to lactic acid. Most of the lactose is removed during the brine process. If the cheese was not salted, the residual moisture contains enough lactose to produce more acid than is ideal for a proper curd ripening.
The second reason for salting cheese is for the cheese flavor. Additionally, for rind cheeses, salting of the cheese will pull moisture from the surface and begin forming the rind of the cheese, which also tend to inhibit growth of many molds.
Additionally, brining is the most efficient means for cooling pasta filata cheese after it has been formed.