Differences in AI Scripts can either screw up your map completely or help the computer from an agonizing defeat. When using the AI Script Area Town, other things happen besides just mining. If it is Zerg, the Overlords will patrol all over their base. If you are trying to activate a cutscene with tranporting units, chances are it will screw up. The only ways to get by this is to use a different color, or set the triggers so that when the transportation units are about to be returned to the base, a unit drops.
Timing is everything here.
You may also notice that sometimes the computer only mines with one or two workers. Anywhere' is a location autmotically put into every map that spans the whole map. I have seen maps where the creator creates another location across the whole map. Certain effects of the computer are always there provided the conditions are right. You can learn them by studying the computer's behavior in a melee.