Who on earth thinks it's a waste of time? I think it's essential for every programmer. I certainly wouldn't consider someone fluent in the language (say, Python

Who on earth thinks it's a waste of time? I think it's essential for every programmer. I certainly wouldn't consider someone fluent in the language (say, Python) until they understand how it is implemented. Also, C++ is arguably faster than C (for the effort put in) and Objective C is a strict superset. Saying either calls into C for performance reasons is pretty silly and doesn't make any sense.