In most authorities in EASA countries you can log PICus hours when you are pilot flying in order to reach the minimum PIC hours for the ATPL requirements.
Actual PIC might have to sign your logbook in that case.
You can usually find the details in your authority website.
Also some airlines are regulating this situation.
All the other boxes are usually not an issue if you are an FO in an airline.
No financial advantages as far as I know, only advantages is to be able to aplly to some companies, which do not accept CPL holder with frozen ATPL. Also you are eligible for an upgrade in a multi pilot aeroplane, for which the full ATPL is a requirement in commercial operations.