ATW patterns like the one Irvin described to you is primarily done so that when the end main strings end at the throat of the racquet, it allows you to string the cross strings from the head to the throat, instead of the throat to head while stringing a one piece pattern.
Your racquet , since it is a Wilson allows stringing from throat to head, but there are a good # of racquets that do not allow that,(example Head, Prince, Yonex), as that places more stress on the racquet and the manuf. specifically does not allow the cross strings to be strung bottom up, and that can effect your warranty if problems arise like breakage.
That said, many stringers either string as 2 piece top down on crosses, or an ATW pattern top down, on all racquets as it is a safer way to string.There are many ATW patterns, and variances of the major ones out there, as they all accomplish the same thing, some of them like the one Irvin described has one tie off on a main, and one tie off on a cross. The ATW patterns I do,(the few I do, as most of my stringing is done 2 piece), ends the tie offs on a top cross, and a bottom cross, so things are a little more symmetrical, but they all accomplish the same goal , which is to allow the cross strings to be strung top down.