Like anything you weigh up the upside against the downside. The downside is more complex code, code that's harder to reason about, the possibility of concurren

Like anything you weigh up the upside against the downside. The downside is more complex code, code that's harder to reason about, the possibility of concurrency bugs, slower development times, the possibility of security flaws and you may just be shifting your performance bottleneck (eg creating a hot mutex). The upside is lower latency, more throughput and higher QPS. My argument is quite simply YAGNI. A lot of these benefits are for many people purely imaginary. They're the very definition of premature optimization. Code that is less complex, faster to develop in and likely "good enough" is probably going to help you way more than that. If you get to the scale where heavy multithreading actually matters, that's a good problem to have. My argument is that many people aren't there and I would hazard a guess that a contributing factor to not getting there is worrying about this level of performance before they need to.