When using a roll-up defined project I find that I often have to add new tasks that are dependent on a existing closed task. Having this dependency will set the Start date of the new task.

Unfortunately Projects does not allow the adding a dependency on a completed task.

The work around is to go back and change the predecessor task to open, then add the dependency for the new task...and then go back and close the predecessor task (and remember to return the predecessor task completed date to the original date).

Very cumbersome.