Thread context switches are pretty expensive. Opinions are pretty divided on this one these days. There was a time when this was very much true but there is so

Thread context switches are pretty expensive. Opinions are pretty divided on this one these days. There was a time when this was very much true but there is some evidence that it is no longer, practically speaking, an issue except in extreme cases. You do pay a cost but it's not immediately obvious that the cost is material. I reach for a threadpool first and async when it becomes clear that I need the extra performance. 99% of the time the threadpool is more than good enough.