You should consider performance/efficiency at all stages. And that consideration should be based on an informed feedback loop where assumptions are validated an

You should consider performance/efficiency at all stages. And that consideration should be based on an informed feedback loop where assumptions are validated and proven empirically. What developers think are performance patterns often wildly diverges from reality. The scenario I gave is when there are performance problems with a developed project (you know -- where a profiler is actually usable, after they already decided on an approach and implemented code) and the developer is effectively guessing at the issues, doing iterative optimize-this-part then run and see if it's fixed pattern. This is folly 100% of the time. Yet it's a common pattern.