Just to not swarm Dave's game topic, here's an article that fully explains this : https://devblogs.microsoft.com/directx/demystifying-full-screen-optimizations/
Just to explain that any performance gap difference in the past has been narrowed a lot in Windows 10 and forward, to the point there's no perceptual difference performance wise in modern systems.
Perhaps it would be best to add this information to the manual, then you could just link manual whenever this question is asked on forums.