When you have a project/task/subtask the time entry links:

project/subtask.

This means you have no idea what task the sub task links to when reviewing the timesheets or the time drop down... which essentially renders the use of sub tasks not possible in the use case where we track time.

In the example in the screenshot you can see the project name and the subtask, but not the actual task. I'll have around 30 tasks and they will all have 01 Copy v01. I'm not going to know which job the time relates to as I work back and forth between the products. I'm already confused and only have a few main tasks so far.

The other screenshot shows the tasks in the task drop down - again not linked to the top level task so you can't tell what it's for.