Use when about to show any prose a human will read - docs, README, commit bodies, UI copy, store text.
Use when building any mechanic that could fail on a machine out of reach - a shipped product, a CLI a user runs, a server.
Use when doing any work in a project that has the instincts plugin installed
Use when touching build scripts, release or packaging steps, publish flows, or CI config.
Use when about to build something someone proposed, especially when the proposer sounds confident and the idea sounds obviously fine.
Use when adding any cross-cutting change - a new gate, limit, permission check, or rule that must apply everywhere.
Use when about to build or agree to build a feature, test, or check, especially when the request sounds big or clever.
Use when a bug surfaces while building on one's own shared code - a library, base class, SDK, or component.