By and large you want to avoid async if you can help it. Sometimes you can’t. The struggles Rustifarians have had with it are a cautionary tale (the stack and borrow checking go together like peanut butter and jelly.). I used to have a lot of fun writing async Python, friends told me I was living dangerously, I finally rewrote my RSS reader/bookmark manager/personal web crawler/image sorter in sync style so some of it could run in Celery and that any blocking on the CPU on a 16 core machine is too much.

People used to worry about the 10k connection problem but machines are bigger now, few services are really that big, and fronting with nginx or something like that helps a lot. (That image sorter serves images with IIS)

JavaScript is async and you gotta live with it because of deployability. No fight with the App Store. No installshield engineer. No army of IT people to deploy updates. “Just works” on PC, Mac, Linux, tablet, game consoles, VR headsets, etc. Kinda sad people are making waitlist forms with frameworks that couldn’t handle the kind of knowledge graph editor and decision support applications I was writing in 2006 but that’s life.