I use subtasks to gather smaller tasks sometimes, like a milestone so to speak, and would love to see the estimated time of all the subtasks be calculated as the estimate of the parent task. It could actually be a new option of "add the total of sub task estimates to the parent" so you could still set the parent estimate if it is something that is itself also work - ie: "Run errands" might be the parent, which likely still needs to account for driving time, as an example, while the sub tasks might be "go to home depot for ___", etc.