Wouldn't it be better to make the 'task' a 'sum of subtasks'

Wouldn't it be better to make the 'task' a 'sum of subtasks'

Perhaps I have the wrong idea on tasks an subtasks, but shouldn't the task be a sum of subtaks. For instance:

  • Clean the office (task)
  •   Clean windows (subtask)
  •   Clean tables (subtask)
  •   Clean coffee machine (subtask)
Currently when I add the task 'clean the office' and state that this takes 'one day' and add the subtasks with durations that equal 2, 4 and 2 hours respectively.

Now when I check the Gantt Chart or the Resource Utilization I see that I'm over-planned because I'm responsible for the Task and the Subtask.

I think it would be a better idea if the main task is a sum of subtasks :-).

Like to here opinions!