Are you thinking that the disapperance of the part of your body will be gone forever? It doesn't work like that. It just make parts of your body like example transfer to a place like what knov's do and make your arm appear again. This ability is inspired by cyberpunk implants like hands with blade inside, it just give you the opportunity to make hidden weapons and a strong restriction but easy to accomplish with you abillity.(your arm is not considered dead) you can make it appear again. Example in order to make the conjured arm appear you shouldn't have an arm, that's why the restriction would be powerful or hard, because how would you do it if you have an arm (well you can cut it) but that's where your ability shows up, to make your arm disappear, and now your counted as a human without arms now you can use your conjuration ability.