A lot of classical culinary traditions, when you trace them back, were born of a very practical obsession with maximizing flavor while minimizing waste. Our culinary forefathers (and they were men, almost exclusively) apparently hated to throw anything away. And since they didn't have refrigerators, they were forced to innovate.
The entire field of garde manger, or cold kitchen, centers upon the idea that nothing gets thrown away and that there is a way to preserve anything without refrigeration.
(A cool room, sure, but no icebox.) This enlightened way of thinking about food is what gave us everyday staples like bacon, sausage and other cured meats, as well as luxuries like pâté de foie gras and peculiarities like the galantine (the classical precursor to the turducken).
Making stock is another example of this. Stock, or fond de cuisine, as it was known, is the basis for sauces, which, especially when seasoned, in turn helped mask the occasionally off flavors of foods that, again because of the lack of refrigeration, well, let's just say, were not always at their peak of freshness.
And the way stocks are made essentially is by simmering bones (veal bones are particularly prized because they are high in cartilage which leads to a richer stock) along with various aromatic vegetables and herbs. Sometimes the bones are roasted first and other times not, which affects the stock's color and flavor.
Bones also contain nutrients, and extracting those nutrients is as much the goal as enhancing flavor.
The reason cartilage is so essential to stock is that when it's simmered, the collagen in the cartilage melts and turn into gelatin, adding body to the stock. This is why stocks often jell when they're chilled.
In any case, once you've made your stock, you might feel inclined to chuck those bones in the bin. They've done their job, right? What good are they now?
Plenty, it turns out. Not content to use these bones just once, our thrifty culinary forefathers invented remouillage (literally, "rewetting" in French), which refers to a stock made by resimmering bones that have been used to make stock once already. "Second stock" it's also sometimes called. And why not? It still beats cooking with water. I'm convinced that some medieval chefs would resimmer those bones until they'd completely dissolved — and still not be happy. In fact, I think I worked for one of them once.
The fact is, you can do this yourself. The fact that bones retain the various properties that produce a good stock even after they've been cooked, roasted, simmered and so on, can work for you just like it worked for those fussy, frugal chefs from days of yore. Suppose every time you cooked a T-bone or porterhouse or any sort of steak or roast with a bone in it, you saved the bone and kept it in the freezer, and then one day pulled them all out and simmered them to make stock?
It's really not so different from what happens when you make turkey soup from a roasted turkey carcass.
It's little habits like these that can help transform your kitchen into a place where magical things happen.