Jim has a great point and I can certainly see folks (on those other websites of course ;)) who are obsesed with small. I can see a few advantages to small: If you are small, a small pack can be more comfortable to carry, A large pack can be obstructive when bushwaking, a tall pack can be unconfortable (I hate have anything behind my head). Otherwise the weight of my pack makes much more difference in my hike than its size.