Context
Most projects arrive as «we need a site, let’s build it». At that point the client is sure the task is simple and the spec is a formality. Two weeks in, «site» turns out to mean a CRM with billing.
What a spec changes
A spec fixes commitments: which routes exist, what happens on form submission, what acceptance criteria look like. It is not a development script or a design — it is a contract.
Effect
After two hours of spec work, a third of the «required» features fall away as «not needed». What remains gets precise definitions.