My understanding is that rolling cache is on disk, which contains photogrammery data that was streamed from Azure cloud. So ‘before and while’ you start flying, data needs to be fetched from Azure cloud. If you already flew there, this data is already in your rolling cache, then the game doesn’t need to fetch it from the cloud, as your disk is faster than the cloud.
The pre-caching that others speak about is when you are flying and the data has ‘already’ been loaded into RAM (either from rolling cache or Azure cloud), post SU5, some of that data is being removed from RAM, as a part of XBox optimization. Most PC users here have lot more RAM to spare and thus don’t want data to be removed from RAM, as it causes popping of artifacts during camera panning. Hope that makes it clear.