I apologize for the sensational and generalizing title. What I'm talking about is focused on web applications, and from empirical data, it seems that most web servers handle very few concurrent requests, therefore it would be silly to go all async to avoid threads.

I'm very surprised that many people here argue that async code is much better to understand than sync code. Ok, so that part is subjective, and let's file it under personal preference. For people who love synchronous coding but fear the cost of threads, I'm trying to make an argument that the fear is probably not justified.