When I sort a view by Importance, which is very useful, levels appear in the list that have no tasks. Strangely, not all levels, just some of them. I'd prefer not to have these cluttering up my screen and occupying space that I could better use by having more tasks displayed before I have to scroll down.
The levels that show up without tasks are ones that had subtasks in them before they got indented inside their parents. View your list flattened out and you'll see. We plan to remove empty dividers in a future update.