Agile Development At Full Stretch
However it’s not uncommon for some teams to estimate on the cautious side. If you find yourself in this situation and finishing the Sprint (or timebox) early, include a couple of nice-to-have “stretch tasks” (or features/stories) in future Sprints.
It’s important to specifically identify them as stretch tasks, i.e. “could haves” in MoSCoW terms (Must-have, Should-have, Could-have, Won’t-have). Make sure no-one is ever beaten up if no stretch tasks are ever achieved in the Sprint. By contrast, do make sure you celebrate as a team if you reach any stretch tasks – even if it’s just a lot of back-slapping and self-congratulation!
And don’t forget to apply the same rules to the stretch tasks as everything else; they must be 100% complete (i.e. shippable) to count.
See also: 10 Key Principles of Agile Development