Obviously such a taboo act as cannibalism should be a last resort but in a world torn apart with suvivors facing the reality of their past actions anything could be put to use
1. Lets say your character is poor after facing a certain defeat or is in an inability to provide for his/herself, well lets also say there is a dead raider right in front of you, while you can take the raider's gear does that quite solve your body's problems? Well you don't see any animals around or anything nearly safe to be edible so put out your shank or knife and start filleting.
2. Just looting a human's corpse could be a good sorce of gaining caps but think about the possibilities of providing to fellow survivors a meat that is less irradiated than your typical brahmin, and if they dont know what such a meat is (Ex: Mystery meat in fallout 3) they will obviously want that meat, at a reasonable price, of course.
3. While leather and synthetic clothing are very nice and even decayed and torn after who knows how many years of abuse after the great war to craft mass bulks of clothing for a business you will need to find something more available than good quality leather or atleast something that could help improve even a small hide of leather,human skin fillers, you see clothing these days with 90% wool or 90% cotton well what about 10% human?our skins may not be as good as a brahmin or as vault jumpsuits but hell any protection counts right?
4.Lets say your a dangerous criminal or well known for your,lets say darker acts,(ex:raiders) or even a survivor that doesnt want to be bothered by such raiders what if you let hang afew body parts or even a corpse of a fallen raider outside your little shack or carried around a head on a stick or hang some by a string on your belt,who wants to mess with you know?