There is an endless variety of things and processes which can be made 'virtual'. Being present, but still not present. In museum contexts, virtuality can be a way of exhibiting representations or copies of objects in which the originals would perhaps not tolerate light, handling, or the inclination to be stolen. Or maybe the original doesn't exist anymore and a reconstruction, diagram or photo can provide understanding of the use, meaning or importance of the object. Or perhaps it is necessary to contextualize material in ways that wouldn't be possible using originals?
Take a look at this virtual book exhibited at the Nobel Peace Center in Oslo. A gimmick, sure, but also a way of activating visitors in their learning experiences. In addition, much more information can be made available in a small space than with traditional techniques.