What is the advantage of using kosher salt
"Kosher" salt has nothing to do with parve rules except maybe in the application of "koshering" AKA dry-brining (as a devout atheist, I haven't a clue on that one). It is coarser than regular table salt (making measurements slightly different) and it contains no added iodine. Certain food snobs (ehem) tend to find it somewhat superior in taste. In general, if the recipe asks for a certain measurement of salt, that means 1.5 times that measurement using kosher salt, hence the need to point it out in recipes if that recipe was developed with kosher salt.