I can see how there are diminishing returns when optimizing but I would never say that server bills are not a metric to be aware of and address. I've always had some idea of what's practically achievable in terms of efficiency within a given architecture and aim for something that gets a good amount of the way there without undue effort. I also enjoy thinking of longer term improvements for efficiency whether that could improve latency or the bottom line and at the same time know that's secondary to providing additional value and gaining customers during a growth period.