Planning should be about choosing tasks, not digging to find out what exactly the customer meant. In my practice, teams that regularly prioritize tasks and keep their list ready for 1.5–2 sprints ahead show 2 times higher predictability of results than those who clarify requirements during the planning itself.

“Plan 80% of the sprint time, and leave the remaining 20% for unplanned tasks.” It is optimal to use retrospective data, not to give 100% load to avoid helplessness in the face of force majeure, and, of course, always keep the focus on value — the sprint goal.