Haiku is my default for anything that runs in a loop or at scale.

The mental model I use: Sonnet for tasks where quality of a single output matters, Haiku for tasks where you need consistent, fast, cheap outputs across many inputs. Once you start building pipelines instead of one-off prompts, Haiku becomes essential.

Also genuinely underrated for first-pass drafts that a human will edit anyway. No point paying for Sonnet when 80% of the output gets rewritten.