When should you chain multiple prompts instead of doing everything in one prompt?

Prompt chaining splits a task into a pipeline of focused steps, e.g. extract -> classify -> draft -> critique -> revise, where each call has a narrow job and its output feeds the next. Chain when the task is complex or multi-stage, when a single prompt tries to do too much and quality drops, when you need to validate or branch on an intermediate result, or when different steps need different tools, models, or temperatures. Chaining makes each step easier to test, debug, and reuse. The costs are added latency, more tokens, and error propagation, since a mistake early cascades downstream, so add validation between steps. Prefer a single prompt for simple tasks where the model handles it reliably in one shot; adding steps then only increases cost and failure surface without improving results.