In reply to MT.

It depends on how you use your system.

David Allen generally doesn't recommend sub-tasks since, usually, the first subtask is the actual next action.

OmniFocus is the same in this case. If you want to have sub-tasks, you can show them in a weird flattened list, but if you use OmniFocus as most people do, meaning you hide groups in contexts list, you won't see them there either, only in the Planning view.

If you use templates in Reminders for your tasks, you may want to read the part on using checklists in the GTD book to give you some ideas for tuning your setup.