My guess would be that macOS shuts down all the additional composition features when full screen is activated so no need for live previews (or even rendering at

My guess would be that macOS shuts down all the additional composition features when full screen is activated so no need for live previews (or even rendering at all) of other windows, all those pretty bokeh effects, etc. Plus it probably means they can switch to a more efficient hardware decoding configuration as they can dump directly to the screen rather than into an application window? I am just guessing though. Interesting that the difference is over 2 hours though, I wouldn't have guessed it would be that much.