Referring to the Colville videos I posted, I think the common thread is that it is the DM's role to create an illusion of depth and player choice whether or not such depth or choice actually exists. So, for example, if you improvise a minor npc in your world, do you feel the need to pretend that was a pre-written part of the campaign world so as to create the illusion of depth (with the players suspending disbelief along the way)? Or, per the example in the latest video, do you have to point to a line in the module to reassure players that the scenario they experienced was not something made up on the spot but rather part of an already existing written scenario? Colville mentions in the video that these things shouldn't matter--and I agree that they shouldn't--but then goes on to just say, but they do, and it's the role of the dm to maintain that illusion of depth.