The main difference is the totality checking. A discriminated union guarantees that you've handled the entire modelled domain (and nothing else); repeated inter

The main difference is the totality checking. A discriminated union guarantees that you've handled the entire modelled domain (and nothing else); repeated interface checking merely guarantees that you've handled a subset of it (and also you may have handled a bunch of other stuff). It's so comforting to know up front that you've done everything you need to do!