If you create qvd files that don't need any transformations in the load script of the presentation layer qlikview documents then you can make sure these qvd files are loaded with optimized load statements. If that happens then the data from the qvd file is read very very fast. See this blog post: http://www.quickintelligence.co.uk/qlikview-optimised-qvd-loads/
Just to make sure this is clear, the optimized load is when you read from a QVD, not when you create a QVD. So if your third layer is the QVW that has the all the charts in it, then that's where you'd ideally have optimized QVD loads. That should be practical since the second layer has already transformed the data, as you'd expect then to only need to load it as is without further transformation into the final QVW. I'm kind of just repeating what Gysbert said.
There is another kind of loading data into a report which could be considered as optimized - the binary load as a third or maybe fourth layer of a data-architecture with generators --> datamodels --> reports.
