What is the advantage of doing that instead of using an IObservable that can filter on the event name in C# or, even better in F#, having an exhaustive pattern

What is the advantage of doing that instead of using an IObservable that can filter on the event name in C# or, even better in F#, having an exhaustive pattern match that automatically casts the argument to the expected type and notifies you at compile time if you forgot to handle some cases?