The two main purposes for wax is to prevent water from penetrating the string fibers and to lubricate. When acting as a lubricant it prevents excess wear on the serving (obviously) and to stop abrasion of the string fibers against each other and at the loops. Wax the whole string. The factory wax does a decent job of protecting the whole string.
Thanks for the reply's guy's, now one more stupid question should it be waxed on or off the bow looks like I have some more thing's to do before the season opens in the morning