Comment by mrkeen

And it's all still true, although I would offer the usual argument that concurrency!=parallelism, and if you reach for threads&STM to try to speed something up, you'll probably have a bad time. With the overhead of GC, STM-retries, false-sharing, pointer-chasing, etc you might have a better time rewriting it single-threaded in C/Rust.

STM shines in a concurrent setting, where you know you'll multiple threads accessing your system and you want to keep everything correct. And nothing else comes close.