Why they call for it? No idea. They taste the same. There are some Jewish rules about its preparation and I think it may have to be blessed or something. More prosaically, its a far more coarse/large crystal salt than table salt and especially sea salt that tends to be fine grain. It also doesn't clump and isn't iodized. Why that makes it more preferable for recipe writers I don't know. (And I just used regular table salt.)