In traditional project management, a parent task is no longer a task as such, but a way of grouping sub-tasks together. Timesheets cannot be assigned directly to a parent task but it will be updated based on the child task(s) progress including timesheets and dates. 

Our customers like to see progress with traditional Gantt views where the parent task is a solid bar grouping the children together.

Project Planning in Odoo is just the worst. Where there are lots of tasks and sub-tasks, It is so hard to keep everything in order, I often feel like abandoning Odoo for any more than the simplest of projects.

Another thing I find bazaar is that in Odoo, a sub-task can be associated with a completely different project. That is just weird and immensely confusing. Can we please get rid of that ... "feature".

I do have more concerns with project such as S-S, S-F, F-F, tasks and more but let's start with the parent-child relationships first.

How do other people use Odoo Project for more traditional larger scaled project?