The first time I tried to make chicken stock it was entirely accidental, and the poor stuff never saw the light of day. During an intro to nutrition class I took sophomore year of college, the teaching assistant told us that chicken bones were high in calcium and edible if boiled until they were soft enough to chew. Excited by this prospect, I dropped some bones into a few cups of boiling water and went to bed. No lid. Without nearly enough water to handle an overnight simmer, the water cooked away and the bones turned to ash. I’ve learned a lot about making chicken stock since then!
Have you ever made chicken stock from scratch? The flavor is much different than anything mass-produced. Plain chicken stock has a subtle flavor with depth. 
Commercial broth comes at you with stronger notes.
Before we go further, here are some definitions as I use them. While these definitions personally help me differentiate parts of soup, other people might assign different meanings to these terms.
Stock has only two ingredients: water and chicken bones.
Soup is the final product served once you simmer stock with vegetables, matza balls, etc.
Broth is the liquid part of soup. If you strain out all the “stuff” — all the vegetables and matza balls, for example — the broth is what’s left.
I use the terms homemade stock and commercial broth because commercial chicken products always have longer ingredient lists: vegetables, natural flavor, salt and more. Stock, as I use it here, is simply tea made with chicken.
In my favorite cookbook, the instructions for chicken stock are similar to what I had tried, though the focus is the liquid, not the bones. I followed this method and succeeded, afterward nibbling the leftover trabecular ends as a prize. Since learning to make stock and finding out how time-consuming the process is, I have found that some soups need the real deal and some are well-suited to commercial.
One recipe in the above-mentioned cookbook has these few ingredients: parsley, spinach, watercress, stock, garlic, salt and pepper. Save for the salt and pepper, there isn’t anything that blends with and disappears into the soup. The lightweight specks of leafy green herbs swirl around and imbue only a subtle flavor to the final broth. Savory and delicate, this soup needs homemade stock. Once, in a pinch, I used two cups of stock and two cups of commercial broth. The soup was totally overpowered by the canned broth. Such a waste of my homemade stock, because I couldn’t even taste it.
On the other hand, some recipes would steamroll a homemade stock. I make a lentil soup that I have only ever tried with commercial because using homemade would actually detract from the flavor. It’s a thick soup stuffed with lentils, carrots, onions and celery. Without the strength of a commercial broth to fight through the legumes and other roughage, it tastes bland.
As a rule of thumb, if a soup has fewer ingredients, use plain stock made only from bones and water. If a soup has more ingredients, use commercial broth. You can work out the specifics depending on your tastes.
