node.js is sexier when it doesn't serve stacktraces in production. Plus async files reads still happen in an internal threadpool (one thread per core, hardcoded, IIRC) so it's pretty easy to saturate that anyway, you should be caching static assets.

The express framework activates the view cache by default when configured for production, so both problems are actually the same.

I suspect it's not configured for prod, since I'm seeing a stacktrace

you are right but I'll still use async over sync anytime... :)

You will often prefer to use sync for one-time loads or for debugging.