Aggregate effort of sub-tasks propageted to the main task

I would be great to have capability of having effort of subtasks aggregated to the effort of the main task.
Otherwise, there is quite hard to estimate the effort of a given task, you need all the time to sum up all numbers, that is ugly. You can monitor progress of finished tasks, but not the time required to finish them.

If that is already requested by another issue (JRA-11697), I apologize for making yet another one.