When you start a sprint, it’s very likely that one or more team members will be on holidays for part of it. How can you still reliably plan a sprint in those circumstances?
Consider creating a vacation user story.
The vacation story has tasks for each team member’s time away, which accounts for some of the team’s capacity when stories are being committed. As the sprint progresses and the vacation days are hit, the burndown chart reflects these time-away tasks as being completed along with any other tasks. This prevents the burn-down from falsely indicating a problem.
When creating a vacation user story the burndown chart will give a better indication of the current progress. In some sprints there will be more people taking days off, like in the summer holiday or during Christmas. This kind of user story can help you in determining how many user stories to take on.
There is a catch, of course, is that this is not an actual user story. It does not add business value :).
Nonetheless, I was intrigued by the thought.