What Are Grafts?
Grafts are special bodily modifications, created through magic and typically used by a small percentage of adventurers who care more about performance or cool abilities than preserving their natural form.
When one kills a monster, something of that monster's essence (a Remnant) attaches to its slayer's spirit, and this Remnant usually forms a Companion. However, some adventurous (read: unscrupulous when experimenting) mages discovered that there was a second option: by using the Remnant as a binding agent, one could take Drops from a monster of the same type as the Remnant and fuse them to a monster slayer, thereby modifying part of the recipient's body! This is Grafting.
Example: Raymond Rex has slain a Chompasaur (a saurian version of a Chomper, basically a poodle-sized 'rex with armor) and has had a novel idea to celebrate his victory: "Hey, since my last name is Rex, maybe I can take this thing's skull and Graft it in as my skull, therefore giving me a cooler head!"
Being an idiot, Raymond follows through with this plan, finding a Grafter in the shady side of town. After he hands over a bag of gold and some assorted Drops (Chompasaur Skull, two Ireful Horns, and some Savage Fangs), the Grafter directs him to a table and straps him down.
Realizing now just how dumb he was, Raymond screams once before the Grafter knocks him out and Grafts the monster drops into his head. Now Raymond wears a Shady Cowl to hide his face, as his once-handsome head now resembles that of a Carnotaurus, horns and all.
What Are The Consequences?
Using Raymond as an example, the most obvious consequences are bodily modification-specifically permanent bodily modification, Grafts can't be removed, only altered or added onto. In Raymond's case, his human head has been modified to mimic a dinosaur's. He retains his memories and human intelligence, his eyesight and hearing, he just has a bit extra, like a keen sense of smell, tetrachromatism, strong jaws and sharp teeth...you get the point, right? Basically, the idea is that the human part is being added onto, not replaced, allowing one to keep the most if not all of the advantages of one's natural parts while gaining new perks.
The not-so-obvious consequences of Grafts are psychological; since Remnants are involved, getting a Graft entails a certain, er, influence. This effect is determined by the Drops used and the parts affected, and for Raymond they'd be:
Chompasaur Skull-Entails a Chomposaur's aggression, predatory instincts, territorialism, and so forth. (Head-related items affect the mind most of all.)
Savage Fangs-The Fangs want to be used, so with them Raymond wants to bite things, chew things, eat things...oh, and they itch irritatingly when Raymond has an opportunity to do these things, like when he's hungry or is offered food. (Fangs, claws, and other miscellaneous parts influence one's native tendencies for use of the body part they're Grafted into, and yes, the itching is a typical problem!)
Ireful Horns-Horns represent power, so with these horns Raymond gains something of the power of a Ire Iguana, specifically their powerful tempers and defensive prowess. This makes him even more aggressive than he would be otherwise, as well as rather defensive and/or paranoid, but it also makes it possible for him to become an Alpha (concept explained here of any group of followers dumb enough to accept him as their leader, as an Ire Iguana's horns symbolize their status in the group.
My question is, What Utility Would Grafts Have In A Medieval Society?
Setting-My setting is essentially medieval Europe, just with monsters like goblins and dragons. This means Christianity can and will come into play, which is probably the biggest hurdle here as far as setting goes. "How dare you get a Graft, Raymond! Know ye not that you have profaned God's creation?!"
Comparing Enchantments-With [Enchantments] already in play, would Grafts still be useful? I think so, as you could have Mothman Wings grafted in to gain flight, as opposed to gaining the Flight Enchantment after slaying several Droppers, and Grafts can graft abilities from a monster that aren't related to an Enchantment but rather to their physiology instead. (After all, Enchantments don't grant you a monster's natural weaponry, but Grafts do!)
However, while Enchantments can be difficult to gain(and requires one to slay multiple members of the same species to max them out), Grafting permanently alters the body and costs gold to pay the mage performing the operation (as opposed to monster hunting, which you can do for basically free if you're willing to take the risk and already have the gear necessary). Additionally, Enchantments don't necessarily have weird side effects like Grafts do, and if you don't want a weird or detrimental Enchantment, you can just kill a monster with regular weaponry and be totally fine.
So, my question restated is simple: Would Grafts Be Useful In a Medieval Fantasy Society, and if so, What Use Would They Have?
Please let me know if question clarification is needed, and thanks for your time and input.