Aesthetics has nothing to do with it. Like Phat said, it is a good way to loose stuff. In addition anything hanging off the pack will cause poor weight distribution and particularly if it dangles, will really result in more energy expended and less comfort. The worst thing is to dangle something off the back of the pack. It is the old "lever arm" - the farther from your back the longer the lever arm and thus the more it will pull you back.

I put EVERYTHING inside, except wet wading shoes. I am not able to get my bear cannister inside laying sideways - I have to have it long dimension up. This is really annoying. Very few packs are designed with the bear cannister in mind. A 2 pound pack vs a 3 pound pack should not be chosen simply on the basis of weight. If the 3 pound pack has a better design, better suspension system and better capacity to get all your stuff inside, go for the 3-pound pack. But bigger is not always better. Take ALL your stuff down to the store and try to pack it before buying any pack.