The first Link trainers did not have any visual display. As everything is harder to do on instruments than with a view, such simulators are very useful for ever

The first Link trainers did not have any visual display. As everything is harder to do on instruments than with a view, such simulators are very useful for everything but initial training and advanced maneuvering (such as aerobatics, combat, in-flight refuelling, and a lot of the things helicopters are used for.)