Form certainly does follow function. Like a beautifully constructed building, a properly constructed leather bag works as it is intended to work, and the shape it takes enables that function.
A backpack, for example, is intended to carry books and gear, and to carry them comfortably. A quality backpack will therefore be large enough to carry these goods comfortably, to carry a sufficient quantity of gear, and to do so with sufficient comfort. Beyond that though, design boils down to much finer details as well. A quality leather backpack will have fine, even stitching, and the stitching will serve to reinforce and hold together the leather in the best possible way. The thread will be an appropriate thickness, to ensure strong seams and long life. The rivets will be secured in the most appropriate parts of the bag, to virtually eliminate the possibility of the bag coming apart. The leather used in the bag will be the most sensible for it’s purpose.
The design of a quality product will be planned and thought out from the smallest detail, to its most general use. This attention to detail inevitably leads to a more time consuming process in creating the product, which inevitably leads to a more expensive product.