Depending on the material chosen, all crowns have a certain thickness to provide sufficient strength against biting forces. The tooth is shaved down enough to compensate for the thickness of the material.
This results in the tooth with a crown not looking bulky but the same size as it was prior to getting the crown. Depending on the material, the reduction of the tooth can be as little as 0.5 mm to at the most 1 mm on the sides and 1-2 mm on the biting surface.