Crushing can also diversify the flavors that alliums contribute to cooked dishes. They’re valuable ingredients in part because their sulfur chemistry suggests and reinforces savory meat flavors. Last year a German study of meat stews found that by far the strongest contributor to the overall “gravy” aroma was an unusual sulfur compound that came not from the meat, but from the onions and leeks. And that compound appears only after these vegetables have been cut up.
From the NYT, here. The entire article is worth reading if you are interested in cooking at all, and especially if you are partial to onions and ginger.