Dishonored 2 questionnnnn

Okay so… I’m not really sure if I get bonecharm crafting? Cause you can sacrifice bonecharms to get traits… and then you make those traits into bonecharms again… but this time they’re included in one bonecharm. Why not just put the bonecharms together? What function does sacrificing them have if I end up using the traits they had anyway? It’s like there’s this unnecessary step in the middle but I could also be missing something o_o