I just spoke at an association meeting where I had set up all my equipment and got everything working just right. Before the event, I made the big mistake of going to the bathroom while other audio visual people were coming into the room. When I returned, my entire setup was moved. They actually picked my table up with my laptop and moved it about 8 feet closer to the screen which made the picture so small no one would have been able to see it. They insisted on using their projector which was a piece of junk (we ended up using mine anyway) and they generally disrupted my entire pre-program setup work.
So, don't leave a careful setup unattended and always be there early to take care of nightmares like this BEFORE the attendees arrive.