Dragon claws are present on nearly all types of dragons. They are one of a dragon's main defenses, although most prefer their breath weapon.
Uses and advantages
Claws are very useful to dragons for several reasons. They can be used for defensive and offensive purposes, like hunting and fighting other dragons. Dragons also find claws useful for tunneling, like King Thrasher, whose claws were enormous and powerful for digging. You can see this in the picture below.
Most dragons have opposable thumbs, which is very useful to them because they can hold objects. A lot of dragon paintings and pictures show them holding objects, such as crystal balls or a tasty-looking knight, with their opposable thumbs.
Claws can be problematic, as many dragon riders have encountered a tendency for sharp claws and spines to slice into the fragile skin of a human. However, earth dragons have perfected the art of carrying a human in a special ridge in their back, which does not have spines.