It is a common practice in most cultures of the world.  There are several theories on the art of shapeshifting and so several varieties of shapeshifting.  The first discussed will be the physical act of shapeshifting.  This is a case in which the user shifts around the physiology of the body to suit the needs of the user.  Examples of this would be a man turning into a cheetah so that he might run quickly, or a wolf so that he might be stronger.  This sort of shapeshifting is quite rare, and usually out of reach for most adepts who are not focused upon that goal.  This is usually something achievable only by shamanic masters and spirits or creatures like the doppelganger.  The second sort of shapeshifting is much more common.  It is when a person or thing changes an aspect of themselves in order to gain certain advantages.  An example would be a person taking on the senses of a wolf, the strength of a bear, or the underwater breathing of a fish.  It could be something as mundane as growing claws to developing the benefits different respiration organs.  One might ask if the observer could see such changes.  The answer would be yes.  Would the changes be overtly physical in actuality?  Usually the answer would be no.  It is a shaping of energy into a specific form and function, and like most magic, remains mostly unseen.  The third kind of shapeshifting is the changing of the avatar, the spirit-self.  Much like the first physical shapeshifting, yet upon the spirit or astral plane.  Which, like all things in such a place, affects to some degree the physical plane.  Giving the user some elements of the first two methods. For any of the shapeshifting methods, adding portions of blood from the creature one wishes to shift into will speed up the process and increase the totality of the change.