PIE means Play In Editor. What I’m asking is how the scene looks when you just hit the green Play button and run the scene as if it was the game. When you launch a Movie Render Queue render, it’s going to “play” your game and then record each frame. So to get some insight into what happens in the MRQ process it’s good to Play your game yourself. For some users this reveals that their exposure starts off wrong and then adapts to the correct level. Or it shows them that their sublevel actually never loads because the default visibility is to be unloaded. Or maybe they are using World Partition Streaming and even though the proper actors are loaded in the viewport, they are not loaded by default. Or you might have some Blueprint logic in the player pawn that actually takes control of the camera or messes up the scene in some other way.
Tl;dr: Playing the game can help debug rendering inconsistencies. MRQ doesn’t just render what’s in your viewport at that moment.