In Danish – as in English - only datid (past) can describe a scene: actions taking place at a given time. Førdatid (past perfect) can’t convey any action but will provide a background for the scene.
Førdatid is often used to sequence a story into situations. The meaning is “having come so far” or “done with that – ready for the next step”:
Da jeg havde været i bad, spiste jeg morgenmad. (When I had showered, I had my breakfast)
Violating this sequence of førdatid/datid by using datid/datid would mean breakfast during the shower:
Da jeg var i bad, spiste jeg morgenmad. (When I was in the shower, I had my breakfast)