One of the features of asynchronous programming in .NET is saving threads during long running operation execution. The FileStream class can be setup to allow asynchronous operations, that allows running (e.g.) a copy operation without virtually using any threads. To my surprise, I found that running asynchronous stream copy performs not only slower, but also uses more processing power than synchronous stream copy equivalent.

Is there any benchmark tests were done to compare a synchronous vs asynchronous operation execution (file, network, etc.)? Does it really make sense to perform an asynchronous operation instead of spanning separate thread and perform synchronous operation in server environment if the asynchronous operation is times slower than the synchronous one?