If you have a numeric column, you can aggregate the values of all broken-down cards automatically using operators like sum, average, etc.
In our workflow, it would be great if we can also aggregate cards with a "Status" column (To-Do, Doing, Done).
For example: the parent card will be automatically put as "Doing" when any of the child cards is in "Doing". The parent card will be in "Done" when all of the child cards are in "Done".
Same thing for the members column: it would be nice if a parent card would automatically get all members assigned to child cards.