Hmm, as I mentioned earlier, these buffer zones came about because of raiding I did with cash earned and no intention of holding the land after it was razed. The troops planted there as rebels do hinder opponents, as do the razed buildings, because as I mentioned earlier, the rebels tend not to build (or rebuild), so any faction that moves in has to build the province themselves. Further, as I recently play GA games, the expansion of my territory is not always necessary.