What are the trade-offs between documenting requirements in detail up front versus refining them progressively through sprints?

1. Detailed up-front documentation gives a stable scope baseline, easier contract and budget management, and a clearer picture of dependencies. It suits fixed-price work, regulated environments, and integrations where another party needs a firm specification.
2. Its costs are real: it assumes the business understands its needs before seeing anything, and every change carries administrative overhead through change control.
3. Progressive refinement responds better to learning. Users see working functionality early, feedback arrives while change is still cheap, and effort is not spent detailing stories that later get deprioritised.
4. Its costs are a less stable scope baseline, more demand on stakeholder availability, and a real risk of losing the end-to-end view if nobody maintains it.
5. In practice I document breadth up front — process maps, objectives, epics, dependencies, non-functional requirements — and depth just in time, refining stories one or two sprints ahead. Non-functional requirements especially need to be captured early, because they are expensive to retrofit.