In your specific example the operation is not asynchronous at all so what you’re doing is async over sync. You’re just releasing one thread and blocking another. There’s no reason to that, because all threads are thread pool threads (unlike in a GUI application).
In my discussion of “async over sync,” I strongly suggested that if you have an API which internally is implemented synchronously, you should not expose an asynchronous counterpart that simply wraps the synchronous method in
Task.Run.
From Should I expose asynchronous wrappers for synchronous methods?
However when making WebAPI calls async where there’s an actual asynchronous operation (usually I/O) instead of blocking a thread that sits and waits for a result the thread goes back to the thread pool and so able to perform some other operation. Over all that means that your application can do more with less resources and that improves scalability.