No no no! Agile has never been about predicting what you will do during a spent and then having slack or crunch time. Agile is about ranking your work by prior

No no no! Agile has never been about predicting what you will do during a spent and then having slack or crunch time. Agile is about ranking your work by priority and dependency, setting meaningful milestones, and then adjusting your estimates frequently to avoid false promises and react to changes in the environment. If you don't finish planned work in a sprint, that is a planning success because after only a brief 2-4 week delay you actually know your performance against estimate and got clear information about how much you can do in a month, and a better chance at estimating what you can deliver next month.