Control disabling means that the control should be visible on screen when it is irrelevant to the situation, but it should be grayed-out and disabled.
If the control is visible on screen even when it is irrelevant to the situation, then the system appears visually consistent, and the users learn about the control's existence before they use it. When the users eventually will need the control, they will find it in the place where they saw it before.
When the control is disabled, the users cannot learn about its function, usage and behavior. The users are aware of the existence of the control, but not of what it can do for them. When the users try a control to learn its function and behavior, they receive no response and they must go to external information resources.
Updated on 29 Feb 2016.