The dilemma is whether to show controls even when they are irrelevant.
If they are visible, the operators becomes aware of them, and get used to their appearance and location on screen. On the other hand, if irrelevant controls are visible on screen, they might interfere with the searching of a relevant control.
If the irrelevant controls do not appear on screen, they do not hamper the operator's perception of the relevant ones. However, on the other hand, the operators might not learn about the invisible controls when the need them, because do not see them beforehand.
Updated on 09 Mar 2016.