You are deciding whether to add "work through this step by step before answering" to a prompt that classifies incoming messages into three categories. What is the relevant trade-off?

The principle — Asking for reasoning is a purchase, not a free upgrade. You pay in tokens and time on every call, and you get a return only when the task actually has steps.

Why the key is correct — Anthropic's guidance states that thinking adds latency and should only be used when it will meaningfully improve answer quality, typically for problems that require multistep reasoning, and advises responding directly when in doubt. A three-way classification of a short message is close to the opposite of that profile: one judgement, no intermediate results. Google's checklist points the same way from another angle, suggesting that where thinking is available you should try prompting without step-by-step instructions and test whether the model's own reasoning beats your prescribed sequence.

Why the others are wrong — The instruction is not free, and on high-volume work the cost recurs on every item. The accuracy benefit is tied to multistep problems rather than being universal. And current guidance discourages layering explicit steps onto a model that already reasons.

Remember this — Ask whether the task has steps. If it does not, reasoning buys latency and nothing else.

Sources — Anthropic, Prompting best practices.