A service blueprint is a wide horizontal map: customer actions on top, front-stage interactions in the middle, back-stage systems and policies at the bottom. It looks like an Excel sheet got into a fight with a flowchart, and that's exactly why it works.
On a recent project, the blueprint surfaced a 12-day government approval step the client had never mentioned in the kick-off. That single discovery shifted the entire UX from "show progress instantly" to "set expectations and stay in touch via email" - a redirection that would have cost weeks if we had jumped straight into Figma.