Nowadays, charcoal briquettes haven't changed much since the late 19th century and the beginning of the 20th century. Modern charcoal briquettes are formed with ingredients mainly from powdered wood charcoal and wood scraps such as sawdust. Charcoal is obtained by burning wood in the absence of oxygen, and charcoal in chunks is the product of that. Since the bulge is charcoal in its most natural form, it's no surprise that purists almost always prefer it.
Beyond that, charcoal in chunks has many attractive qualities: it ignites faster, burns longer and leaves behind very little ash compared to briquettes. Chunked charcoal also responds better to oxygen, making it easier to control the temperature of the fire if the grill has adjustable vents. Charcoal is a natural mineral that forms over millions of years, while charcoal is a manufactured product created from wood. While charcoal in its natural state is never used alone in a barbecue or smoker, it is commonly added to charcoal briquettes to increase energy density.
The briquettes, on the other hand, are made of sawdust, scraps of wood and anthracite. During the manufacturing process, binders and additives are added to hold the material together and facilitate its illumination. It will then go through a process very similar to that of charcoal in pieces, in which it is heated to high temperatures in an environment with little oxygen. That said, some types of charcoal give off much more heat than charcoal.
It's no secret that many manufacturers of charcoal for barbecue add anthracite, a pure form of charcoal with another biomass, to their mix to increase the energy density of charcoal briquettes.