One more datapoint here. Good performance helps avoiding scaling problems. One example is an API I recently wrote. I was initially in Python and performance was OK I guess. I had to take care of horizontal scaling, how to manage the infrastructure, a bit of distributed scaling and all the other goodies that come along. By rewriting it in Rust and caring about performance I was able to run it on a single machine (which is ok for that product). That saved me quite some hustle. And my average response time went from 300ms to 29ms.

If the app would scale a lot I would still need to go into all that trouble but at this early stage the benefits of really simple infrastructure is immense.