I worked there too and you're talking about performance in terms of optimal usage of CPU on a per-project basis.

Google DID put a ton of effort into two other aspects of performance: latency, and overall machine utilization. Both of these were top-down directives that absorbed a lot of time and attention from thousands of engineers. The salary costs were huge. But, if you're machine constrained you really don't want a lot of cores idling for no reason even if they're individually cheap (because the opportunity cost of waiting on new DC builds is high). And if your usage is very sensitive to latency then it makes sense to shave milliseconds off because of business metrics, not hardware $ savings.