There is this sad idea that "threads are bad" and that event is the cat's pajamas. But even nginx admits that there are situations where threads make sense, hence their semi-recent addition to adding them.

I encourage people to read http://capriccio.cs.berkeley.edu/pubs/threads-hotos-2003.pdf. Yeah, it's old, but so is the 10k Concurrency paper which is still touted as the reason why people should use nginx instead of anything else. Threads will only get better.