Count Leaves Column
The Count Leaves column allows you to quickly see how many sub-items of an issue are at the last level of the hierarchy (they have no sub-items of their own). This is particularly useful when you have organized issues using Group generators or Flex Items and you need to count just the issues themselves.

Notice in the example above that the Big Project group has 5 sub-items, but only 4 leaves. The Count Leaves column allows you to omit group items (in this case, the sprint groups) and look just at the number of issues in the last level of the structure's hierarchy.
See also: Count Sub-Items Column