You must save the journal receivers when they are no longer attached, so that you have all the journal entries saved.
Using a save-while-active operation to save objects before they reach a commitment boundary can result in objects that are saved with partial transactions. Saving journal receivers ensures that they are available to recover objects that are restored with partial transactions.
When you save a journal receiver that is no longer attached, you can free storage. However, a journal receiver whose storage has been freed must be restored before you can use it for recovery.