It’s important for a coffee bean to increase its mass when during the roast. When brewing coffee, well expanded coffee beans would let water go through deep within its tissue, and the resulting cup has better coffee extraction.
The way coffee bean sold now possibly affects the bean quality negatively. As you know, most of bean shops sell coffee based on its weight. So if coffee is sold based on its volume rather than its weight, the coffee industry would focus on how well they can expand the coffee volume, and the cup quality could improve… I assume.
The difficulty of the coffee roasting is this balance. Roasting lightly doesn’t get ideal coffee bean expansion, but too much emphasis on bean expansion could lead to the over roast.
In addition, cooling down a roasted bean is also important part of the roasting process. It doesn’t affect much to American roast, but such deep roasts as French or Italian roasts are all about how quickly the bean could be cooled. Otherwise, the bean gets over roasted. No one likes burnt coffee.