Showing or not cables on stage is a matter of style, not of efficiency. Not only it is untidy and sometimes disturbing for the viewer to see cables running all over the place (power and extension cords, laptop and audio/video cables, etc) but it can also be dangerous for speakers and technicians, as they might trip over them.
There are many solutions to avoid showing your cables:
- hide them from the public eye (though like this you don’t solve the safety issues for speakers and technicians working on stage)
run them behind the stage or under a layer of carpet. Alternatively one of the most practical solutions is to use cable floor-ducts that are sturdy and visible enough to be walked over safely
- some stages have wholes to run cables underneath and make them come to surface in the required spots
The following are some photos taken at a conference last week. I was sitting in one of the first rows and it was rather disturbing to see all those hectic powercords running all over the place.