Async code can scale essentially infinitely, because it can multiplex thousands of Futures onto a single thread. And you can have millions of Futures multiplexed onto a dozen threads.

This makes async ideal for situations where your program needs to handle a lot of simultaneous I/O operations... such as a web server:

http://aturon.github.io/blog/2016/08/11/futures/

Async wasn't invented for the fun of it, it was invented to solve practical real world problems.