What are the uses of rocks in construction as cladding?

There are two major uses that cladding has. Keep in mind that the use of rocks is just the material of choice in this case.

First, cladding is used as a durable and/or protective layer over your building membrane. In older or more advanced examples it may also be or include the membrane. (The building membrane, in this case, would be the water and/or air barrier system such as building felt or Tyvek.)

Second is just aesthetics. People like the way it looks, and reminds them of classic archetypes.